chore: untrack Playwright MCP captures and root screenshot; trim docker build context

Also records the gitea runner durable fix in the launch checklist.

.dockerignore

@@ -10,3 +10,11 @@ k8s
 .DS_Store
 .env
 .env.*
+# Not needed to build the site; keeps the build context small
+.playwright-mcp
+# root-level screenshots only (dockerignore *.png does not match in subdirectories)
+*.png
+planning
+tests
+test-results
+playwright-report