feat(chat): show persistent session token usage

[dawNotPoi]

Summary

• Keep current-conversation token usage visible in the composer status row.
• Show the full breakdown in wide panels and a compact total/cache-hit summary in narrow or tiled panels.
• Reuse the existing context/token popover, hide unavailable cache counters, and share one usage subscription across both indicators.
• Add the short token unit to all 10 locale bundles.

Verification

• pnpm test — 520 files, 7,776 tests passed.
• pnpm build — production static export passed (34/34 pages).
• pnpm eslint . and Prettier checks passed.
• Rebased onto current main, retaining the stable composer wrapper added upstream and applying the container query only while the status row is attached.

Closes #748

[dawNotPoi]

@xintaofei I rebased this PR onto current main, and GitHub now shows it as mergeable. The composer keeps a persistent per-conversation token summary, with a compact layout for narrow panels and one shared usage subscription. The conflict resolution retains upstream's stable block composer wrapper and enables the size container only while the status row is attached. All 7,776 tests, the production build, ESLint, and Prettier pass locally; cross-platform CI is running. The PR description has the scope and verification details. Ready for review when convenient.