feat: add CI pipeline with ESLint, refactor deploy with rollback + Telegram

- Add eslint.config.mjs (flat config, eslint-config-next@16 + TypeScript)
- Add .gitea/workflows/ci.yaml (lint, test:unit, build on all branches)
- Refactor deploy.yaml: needs: [ci] gate, Docker rollback tag, Telegram notifications
- Fix 3 pre-existing lint errors (empty interfaces, ts-ignore, require imports)

memento-note/components/note-card.tsx

@@ -197,6 +197,7 @@ export const NoteCard = memo(function NoteCard({
   const sanitizedHtml = useMemo(() => {
     if (note.type !== 'richtext' || !note.content) return ''
     if (typeof window !== 'undefined') {
+      // eslint-disable-next-line @typescript-eslint/no-require-imports
       return require('isomorphic-dompurify').sanitize(note.content)
     }
     return note.content