Summary

This PR completes the P1 session usage reporting work and localizes the built-in Commit / Create PR quick actions.

It makes session usage reports rely on persisted runtime facts instead of only best-effort tool traces, adds a richer Chat/detail UI for inspecting usage, files, tools, errors, and slow spans, and improves the UX around incomplete or legacy report data.

What Changed

Runtime Usage Data

• Persist richer session usage facts from runtime events, including model rounds, token usage, tool execution timing, and file-related activity.
• Extend session history/API contracts so usage reports can reconstruct more reliable per-session statistics.
• Prevent the local usage-report action itself from polluting the measured session span.
• Add report coverage/accounting metadata so the UI can clearly communicate when data is complete, partial, approximate, or unavailable.
• Improve legacy/missing model identity handling so old sessions no longer show unclear labels such as model round 0.

Chat Usage Report UX

• Move the usage report entry point into the Chat input footer.
• Add a compact session usage card in Chat with clearer metrics, token labels, file summaries, tool summaries, and detail-entry affordances.
• Make the usage report action visually lighter and theme-aware while keeping it discoverable.
• Keep unavailable token/model values from being combined with misleading token units.

Detail Panel

• Add a tabbed session usage detail panel for overview, models, tools, files, errors, and slow spans.
• Add snapshot-backed file diff actions from the files tab.
• Make file paths compact in tables/cards while preserving full paths in tooltips.
• Improve long-table ergonomics so the diff action remains reachable.
• Add turn-jump behavior for slow spans where a concrete session turn exists.
• Improve missing-duration and unavailable-data presentation with quieter visual treatment and explanatory tooltips.

Localization

• Add/adjust English, Simplified Chinese, and Traditional Chinese copy for the new usage report UI.
• Normalize the usage metric label to Tokens.
• Localize built-in Commit and Create PR quick action labels/prompts through reusable quick-action localization helpers.

Documentation

• Update the session runtime usage report design document with the current P1 implementation shape, entry point, known coverage boundaries, and follow-up direction.

Reviewer Notes

• The branch is intentionally split into three commits:
  1. feat(usage): persist runtime report facts
  2. feat(usage): add report details and diff actions
  3. feat(i18n): localize quick action labels
• The usage report still exposes coverage/accounting state because some historical sessions or providers may not have complete runtime metadata.
• Existing Rust checks currently report a pre-existing unused import warning in src/apps/desktop/src/tray.rs; this PR does not modify that area.

Validation

• pnpm run lint:web
• pnpm run type-check:web
• pnpm --dir src/web-ui run test:run
• cargo check --workspace
• cargo test --workspace
• git diff --check origin/main..HEAD