ci(gitea): shared composite actions + pipeline generator for Gitea Actions

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AqpXh3hQMMaC74pTjFq4it

Gitea 1.25 cannot run reusable workflows (workflow_call), so the logic of
deploy-app.yml, smoke.yml and ci.yml moves into composite actions under
.gitea/actions/, and each repo gets a thin pipeline rendered by
tools/gitea-pipeline/render.py from repos.json. .github/workflows is left
untouched (Gitea ignores it once .gitea/workflows exists).

.gitea/actions/ci-lint-php/action.yml

@@ -0,0 +1,24 @@
+name: CI - PHP lint
+description: PHP syntax check (Gitea port of the lint-php job in the reusable ci.yml).
+inputs:
+  php:
+    required: true
+runs:
+  using: composite
+  steps:
+    - name: Setup PHP ${{ inputs.php }}
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: ${{ inputs.php }}
+        coverage: none
+    - name: Syntax check all PHP files
+      shell: bash
+      run: |
+        set -e
+        find . -name '*.php' \
+          -not -path './vendor/*' \
+          -not -path './node_modules/*' \
+          -not -path './.git/*' \
+          -not -path './.github/*' \
+          -not -path './.gitea/*' \
+          -print0 | xargs -0 -r -n1 -P4 php -l > /dev/null