ci(linux): migrate PR builds to build-citron-linux.sh, remove Arch container, and clean up obsolete scripts

build-linux.yml:
- Replace per-workflow build/package shell scripts (build-citron.sh,
  get-dependencies.sh, package-citron.sh) with a unified call to
  build-citron-linux.sh from the emulator repo, which handles dependency
  setup, CPM build, and AppImage/tar.zst packaging in one script
- Remove Arch Linux container (ghcr.io/pkgforge-dev/archlinux:latest)
  from the linux build job; the job now runs directly on the Ubuntu
  GitHub-hosted runner, eliminating the nested container layer
- Remove the 'Install Git' step (pacman -Syu git) that was only needed
  inside the Arch container
- Remove the 'Install Packaging Dependencies' step (pacman gamemode)
  that was only needed inside the Arch container; gamemode handling is
  now delegated to build-citron-linux.sh

Deleted files:
- build-citron.sh: Arch-based build script replaced by build-citron-linux.sh
- get-dependencies.sh: Arch pacman dependency installer, superseded
- package-citron.sh: Arch-based AppImage/tar.zst packager, superseded
- PKGBUILD: unused Arch Linux package build descriptor

README.md:
- Rewrite to reflect this repo's purpose as a PR test-artifact builder,
  not a nightly/stable release repo; redirect users to citron-neo/CI
  for releases
- Describe the per-platform workflow_dispatch model: takes branch, PR
  number, and head repo as inputs; posts/updates a results comment on
  the PR with per-platform status and nightly.link download links
- Document build-deduplication: skips re-building a commit already
  successfully built for that platform
- Update title and badge references from 'Citron' to 'Citron Neo'
- Mention tar.zst portable archive produced alongside the AppImage
- Update AppImage section with uruntime fuse3/no-fuse compatibility notes
- Replace bullet lists with dash lists; remove star history block,
  raison d'etre image, and Pkgforge attribution section

.github/workflows/build-linux.yml

@@ -179,6 +179,9 @@ jobs:
     if: always() && needs.check-version.outputs.should_build == 'true'
     runs-on: ${{ matrix.os }}
     timeout-minutes: 120
+    env:
+      CPM_SOURCE_CACHE: ${{ github.workspace }}/.cpm-cache
+
     strategy:
       fail-fast: false
       matrix:
@@ -187,28 +190,23 @@ jobs:
             os: ubuntu-latest
             artifact_name: "Artifacts_x86_64"
             script_suffix: ""
-            build_arg: ""
+            arch_arg: ""
           - name: "Citron Build (Optimized x86_64)"
             os: ubuntu-latest
             artifact_name: "Artifacts_v3"
             script_suffix: "_v3"
-            build_arg: "v3"
+            arch_arg: "--arch v3"
           - name: "Citron Build (aarch64)"
             os: ubuntu-24.04-arm
             artifact_name: "Artifacts_aarch64"
             script_suffix: ""
-            build_arg: ""
-
-    container: ghcr.io/pkgforge-dev/archlinux:latest
+            arch_arg: ""
 
     steps:
-      - name: Install Git
-        run: pacman -Syu --noconfirm --needed git
-
-      - name: Checkout Workflow Scripts
+      - name: Checkout CI Scripts
         uses: actions/checkout@v4
 
-      - name: Clone Citron Source Code
+      - name: Clone Citron Source
         shell: bash
         run: |
           CLONE_REPO="${{ needs.check-version.outputs.head_repo }}"
@@ -216,10 +214,9 @@ jobs:
           EXPECTED_HASH="${{ needs.check-version.outputs.new_hash_full }}"
           if [ -z "$CLONE_REPO" ] || [[ "$CLONE_REPO" != *"/"* ]]; then CLONE_REPO="${{ env.UPSTREAM_REPO }}"; fi
           if [ -z "$BRANCH_NAME" ]; then BRANCH_NAME="main"; fi
-
           echo "Cloning from $CLONE_REPO (branch: $BRANCH_NAME)..."
-          git clone --recurse-submodules --shallow-submodules --depth 1 -b "$BRANCH_NAME" "https://github.com/${CLONE_REPO}.git" emulator
-          cd emulator
+          git clone --depth 1 -b "$BRANCH_NAME" "https://github.com/${CLONE_REPO}.git" citron
+          cd citron
           ACTUAL_HASH=$(git rev-parse HEAD)
           echo "Checked out ${CLONE_REPO}@${BRANCH_NAME}: ${ACTUAL_HASH}"
           if [ -n "$EXPECTED_HASH" ] && [ "$ACTUAL_HASH" != "$EXPECTED_HASH" ]; then
@@ -227,51 +224,54 @@ jobs:
             exit 1
           fi
 
-      - name: Prepare Build Environment
-        run: |
-          mv get-dependencies.sh emulator/
-          mv build-citron.sh emulator/
-          mv package-citron.sh emulator/
-
-      - name: Add Git Safe Directory
-        working-directory: ./emulator
+      - name: Set Git Safe Directory
+        working-directory: ./citron
         run: git config --global --add safe.directory "$PWD"
 
-      - name: Install dependencies
-        working-directory: ./emulator
-        run: chmod +x ./get-dependencies.sh && ./get-dependencies.sh
+      - name: Cache CPM Sources
+        uses: actions/cache@v4
+        with:
+          path: ${{ github.workspace }}/.cpm-cache
+          key: cpm-linux-${{ runner.os }}-${{ matrix.os }}-${{ hashFiles('citron/CMakeModules/dependencies.cmake') }}
+          restore-keys: |
+            cpm-linux-${{ runner.os }}-${{ matrix.os }}-
 
-      - name: Build Citron from source
-        working-directory: ./emulator
+      - name: Setup Build Environment
+        working-directory: ./citron
+        run: |
+          chmod +x ./build-citron-linux.sh
+          ./build-citron-linux.sh setup
+
+      - name: Compute Version
+        id: version
+        working-directory: ./citron
+        run: |
+          GIT_SHA="$(git rev-parse --short HEAD)"
+          PR_NUMBER="${{ needs.check-version.outputs.pr_number }}"
+          if [ -n "$PR_NUMBER" ]; then
+            echo "app_version=PR-${PR_NUMBER}-${GIT_SHA}" >> $GITHUB_OUTPUT
+          else
+            echo "app_version=${GIT_SHA}" >> $GITHUB_OUTPUT
+          fi
+          echo "sha=${GIT_SHA}" >> $GITHUB_OUTPUT
+
+      - name: Build Citron
+        working-directory: ./citron
+        env:
+          APP_VERSION: ${{ steps.version.outputs.app_version }}
+          ARCH_SUFFIX: ${{ matrix.script_suffix }}
+          DEVEL: "true"
         run: |
           NPROC_VAL=$(nproc --all)
           JOBS_VAL=$((NPROC_VAL > 4 ? 4 : NPROC_VAL))
-          chmod +x ./build-citron.sh
-          JOBS=${JOBS_VAL} DEVEL=true ./build-citron.sh ${{ matrix.build_arg }}
-
-      - name: Package AppImage with Correct Name
-        working-directory: ./emulator
-        run: |
-          GIT_SHA=$(git rev-parse --short HEAD)
-          PR_NUMBER="${{ needs.check-version.outputs.pr_number }}"
-          BRANCH_NAME="${{ needs.check-version.outputs.branch_name }}"
-          SAFE_BRANCH=$(printf '%s' "$BRANCH_NAME" | tr '/ ' '--' | tr -cd 'A-Za-z0-9._-')
-          if [ -n "$PR_NUMBER" ]; then
-            export APP_VERSION="PR-${PR_NUMBER}-${GIT_SHA}"
-          else
-            export APP_VERSION="${SAFE_BRANCH:-main}-${GIT_SHA}"
-          fi
-          export VERSION="${APP_VERSION}"
-          export ARCH_SUFFIX="${{ matrix.script_suffix }}"
-          export DEVEL="true"
-          chmod +x ./package-citron.sh
-          ./package-citron.sh
+          JOBS=${JOBS_VAL} ./build-citron-linux.sh use --pgo none --lto full ${{ matrix.arch_arg }}
 
       - name: Upload Artifacts
         uses: actions/upload-artifact@v4
         with:
           name: ${{ matrix.artifact_name }}
-          path: emulator/dist/
+          path: citron/build/use-nopgo/AppImage/
+
 
   comment-end:
     name: Comment End
@@ -301,7 +301,7 @@ jobs:
               gh api -X DELETE "repos/${UPSTREAM}/issues/comments/${DUPLICATE_ID}" >/dev/null 2>&1 || true
             fi
           done
-          
+
           if [ -n "$COMMENT_ID" ]; then
             LOG_URL="https://github.com/${REPO}/actions/runs/${RUN_ID}"
             COMMIT_LINK="[\`${HASH_SHORT}\`](https://github.com/${HEAD_REPO}/commit/${HASH_FULL})"