ci: add Gitea Actions workflows for build + EasyPanel deploy

Two workflows under .gitea/workflows/:

- build-and-deploy.yml: on push to source-code, install deps, run
  astro build, then POST the dist/ SHA + ref to EASYPANEL_WEBHOOK_URL
  (read from repo secret) so EasyPanel redeploys. Uploads dist/ as a
  7-day artifact as a fallback. Gracefully warns if the secret is empty
  so contributors can run the build job without breaking.

- lint.yml: lightweight build check on every push + PR so syntax /
  missing-image errors surface before the deploy workflow runs.

To enable auto-deploy:
  1. Set EASYPANEL_WEBHOOK_URL secret in Gitea repo settings
  2. Configure EasyPanel service to source from this repo + branch
     source-code, build command 'npm run build', output 'dist'

.gitea/workflows/lint.yml

@@ -0,0 +1,22 @@
+name: Lint & Test
+
+on:
+  push:
+    branches:
+      - source-code
+  pull_request:
+    branches:
+      - source-code
+
+jobs:
+  build-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+      - run: npm ci --no-audit --no-fund
+      - name: Build (catches syntax + missing-image errors before deploy)
+        run: npm run build