fix: use GITHUB_RUN_NUMBER for Forgejo job URLs and pin Bun version in CI

Forgejo uses the per-repo sequential run index (GITHUB_RUN_NUMBER) in
action URLs, not the internal DB run ID (GITHUB_RUN_ID). This caused
"View job" links to return 404. Fixed in all 4 URL construction sites:
create-initial comment, update-comment-link, and both prompt generators.

Also pins Bun to 1.2.21 in CI — Bun 1.3.9 broke spyOn(fs, ...) which
failed 18 upstream image-downloader tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.forgejo/workflows/ci.yml

@@ -13,6 +13,11 @@ concurrency:
   group: ci-${{ github.ref }}
   cancel-in-progress: true
 
+# Pin Bun version across all jobs. Bun 1.3.x broke spyOn(fs, ...) in tests.
+# Bump this when upstream tests are updated for newer Bun versions.
+env:
+  BUN_VERSION: "1.2.21"
+
 jobs:
   test:
     runs-on: grunt
@@ -25,9 +30,16 @@ jobs:
       - name: Install Bun
         run: |
           if command -v bun &> /dev/null; then
-            echo "Bun already installed: $(bun --version)"
+            INSTALLED=$(bun --version)
+            if [ "$INSTALLED" = "$BUN_VERSION" ]; then
+              echo "Bun $BUN_VERSION already installed"
+            else
+              echo "Bun $INSTALLED installed, need $BUN_VERSION — reinstalling"
+              curl -fsSL https://bun.sh/install | bash -s "bun-v${BUN_VERSION}"
+              echo "$HOME/.bun/bin" >> "$GITHUB_PATH"
+            fi
           else
-            curl -fsSL https://bun.sh/install | bash
+            curl -fsSL https://bun.sh/install | bash -s "bun-v${BUN_VERSION}"
             echo "$HOME/.bun/bin" >> "$GITHUB_PATH"
           fi
 
@@ -56,9 +68,16 @@ jobs:
       - name: Install Bun
         run: |
           if command -v bun &> /dev/null; then
-            echo "Bun already installed: $(bun --version)"
+            INSTALLED=$(bun --version)
+            if [ "$INSTALLED" = "$BUN_VERSION" ]; then
+              echo "Bun $BUN_VERSION already installed"
+            else
+              echo "Bun $INSTALLED installed, need $BUN_VERSION — reinstalling"
+              curl -fsSL https://bun.sh/install | bash -s "bun-v${BUN_VERSION}"
+              echo "$HOME/.bun/bin" >> "$GITHUB_PATH"
+            fi
           else
-            curl -fsSL https://bun.sh/install | bash
+            curl -fsSL https://bun.sh/install | bash -s "bun-v${BUN_VERSION}"
             echo "$HOME/.bun/bin" >> "$GITHUB_PATH"
           fi
 
@@ -79,9 +98,16 @@ jobs:
       - name: Install Bun
         run: |
           if command -v bun &> /dev/null; then
-            echo "Bun already installed: $(bun --version)"
+            INSTALLED=$(bun --version)
+            if [ "$INSTALLED" = "$BUN_VERSION" ]; then
+              echo "Bun $BUN_VERSION already installed"
+            else
+              echo "Bun $INSTALLED installed, need $BUN_VERSION — reinstalling"
+              curl -fsSL https://bun.sh/install | bash -s "bun-v${BUN_VERSION}"
+              echo "$HOME/.bun/bin" >> "$GITHUB_PATH"
+            fi
           else
-            curl -fsSL https://bun.sh/install | bash
+            curl -fsSL https://bun.sh/install | bash -s "bun-v${BUN_VERSION}"
             echo "$HOME/.bun/bin" >> "$GITHUB_PATH"
           fi