feat(deploy): build+push release image on every merge to main

Was tag-push-or-manual-dispatch only. Adds a push:main trigger so main stays
continuously deployable without needing a version tag for every change.

Also fixes a real bug this surfaced while testing the D17 registry-TLS fix:
the old tag logic unconditionally retagged :latest on every run, including
manual test dispatches off a feature branch — one such dispatch, done while
verifying the previous commit, silently overwrote :latest with a
feature-branch build. Tag resolution now only moves :latest on an actual
main push or a version tag; a manual dispatch gets its own
manual-<timestamp>-<sha> tag and leaves :latest alone.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R2ZKeWkZV7ehf7fivrAkkG

.gitea/workflows/release.yml

@@ -2,6 +2,7 @@ name: Release image
 
 on:
   push:
+    branches: [main]
     tags: ['v*']
   workflow_dispatch:
 
@@ -36,20 +37,36 @@ jobs:
           username: BBergle
           password: ${{ secrets.REGISTRY_TOKEN }}
 
-      - name: Resolve image tag
+      # `latest` should only ever mean "what's actually on main" (or a tagged release) — not
+      # whatever a manual test dispatch off some feature branch happened to build. Learned the
+      # hard way: a manual dispatch off this very branch, while verifying the fix above, silently
+      # overwrote `latest` under the old unconditional-tags logic. Building the full tag list here
+      # in bash (rather than a conditional expression inline in the tags: block below) means there's
+      # never a blank line for build-push-action to choke on when latest isn't included.
+      - name: Resolve image tags
         id: tag
         run: |
+          IMG=registry.bbergle.com:9537/bbergle/bike-app
           if [ "${{ gitea.ref_type }}" = "tag" ]; then
-            echo "value=${{ gitea.ref_name }}" >> "$GITHUB_OUTPUT"
+            VALUE="${{ gitea.ref_name }}"
+            UPDATE_LATEST=true
+          elif [ "${{ gitea.ref_name }}" = "main" ] && [ "${{ gitea.event_name }}" = "push" ]; then
+            VALUE="main-$(git rev-parse --short HEAD)"
+            UPDATE_LATEST=true
           else
-            echo "value=manual-$(date -u +%Y%m%d%H%M%S)" >> "$GITHUB_OUTPUT"
+            VALUE="manual-$(date -u +%Y%m%d%H%M%S)-$(git rev-parse --short HEAD)"
+            UPDATE_LATEST=false
           fi
+          {
+            echo "tags<<EOF"
+            echo "$IMG:$VALUE"
+            [ "$UPDATE_LATEST" = true ] && echo "$IMG:latest"
+            echo "EOF"
+          } >> "$GITHUB_OUTPUT"
 
       - uses: docker/build-push-action@v6
         with:
           context: .
           file: Dockerfile
           push: true
-          tags: |
-            registry.bbergle.com:9537/bbergle/bike-app:latest
-            registry.bbergle.com:9537/bbergle/bike-app:${{ steps.tag.outputs.value }}
+          tags: ${{ steps.tag.outputs.tags }}