Add a dedicated pi agent usage collector

[surim0n]

Summary

Fixes #8270.

Add a dedicated local Pi/Oh My Pi usage record for every backend, including OpenRouter. Claude and Codex no longer aggregate Pi/OMP transcripts; native and opencode collection remains intact.

Changes

• Discover default/configured session directories, Pi/OMP profiles, the explicit Pi session-directory override, and OMP XDG locations.
• Count physical aliases and inherited fork responses once using lineage-scoped response identity, not globally unique short IDs. Cover OMP cost-reset forks and missing UUID parents.
• Preserve exclusive per-response token categories and local-calendar windows; skip malformed records, counters, dates and parent paths.
• Make caching optional, serialized, date/root-aware, and safe after empty forced scans or failed writes. Invalidation is best effort if the filesystem refuses both replacement and deletion.
• Invalidate Codex caches from before the Pi split to prevent transitional double counting.
• Label the record Local usage, not Subscription, and update existing documentation.

Validation

• 25 Pi regressions plus the original four scanner assertions pass in UTC and Pacific/Kiritimati (UTC+14).
• Claude, Codex, Claude limits, Fireworks, updater, agents-panel, plugin validation and first-party manifest schema suites pass in isolated Bash 5/Linux tests.
• Full test/cli, metadata validation, Python compilation and git diff --check pass. Minimal-container CLI runs emit existing missing-theme-directory warnings. No full test/all pass is claimed.
• Real updater integration discovers and writes pi.json; extracted panel functions select Local usage and make a nonempty record visible.
• No live Quickshell/graphical acceptance run is claimed.

Coordination

Related active work: #8602 (fork deduplication), #9546 (profiles), #8345 (roots/cache identity), and #8649 (OMP collector). After this split, Pi fixes must target the dedicated collector rather than unused Claude/Codex Pi scanners. Agree on OMP ownership before adding another record.

Generated with Devin

[surim0n]

Pushed f481aa5 after a deeper audit. Added cache/date/write-failure regressions, malformed-record handling, configured roots/profiles, fork and physical-alias deduplication, and Codex cache-transition coverage. All 25 Pi tests plus the original assertions pass in UTC and UTC+14; adjacent collector/updater tests and the CLI suite pass in isolated Linux. The description documents validation limits and overlap with #8602, #9546, #8345 and #8649. Pi is labeled Local usage; no quota or cost is inferred.