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-history-modal.tsx

@@ -85,6 +85,7 @@ function VersionPreview({ entry, language }: { entry: NoteHistoryEntry; language
               <MarkdownContent content={entry.content || ''} />
             </div>
           ) : isRt ? (
+            // eslint-disable-next-line @typescript-eslint/no-require-imports
             <div dangerouslySetInnerHTML={{ __html: require('isomorphic-dompurify').sanitize(entry.content || '') }} />
           ) : (
             <pre className="whitespace-pre-wrap font-sans">{entry.content || ''}</pre>