v0.9.4 - server-owned chat titles

What's Changed

• Moved web chat title generation into the server chat lifecycle, generated from the first persisted user message.
• Removed the client-triggered title endpoint path and the first-message fallback write; null titles stay as Untitled until a generated title is persisted.
• Kept delivery on ordinary chat-list invalidation, with browser tab title sync and local-only sidebar title reveal.
• Tightened title persistence and added focused title helper tests.
• Bumped the default app image tag in compose.yml to 0.9.4.

Validation

• npm run test -w apps/web --
• npm run lint -w apps/web --
• npm run lint -w apps/mobile --
• npm run build -w apps/web --
• docker build -t overtchat:web-title-generation-check .
• GitHub Web E2E Smoke passed on PR #54, main, and the v0.9.4 tag.
• Build and publish app image passed for v0.9.4, publishing ghcr.io/yoloyash/overtchat-app:0.9.4 and latest.