Fix T3 import reliability and surface provider usage

[sbbedefended]

Summary

• make legacy T3 import reliable by importing full thread state in bulk and preserving thread/message metadata
• stop implicit startup migration from ~/.t3 so import only happens through explicit DP Code actions
• surface real provider usage in the UI, including the branch toolbar panel and optional composer badge

Details

• add orchestration.importLegacyT3State plus the server-side importer and schema repair migration for legacy projection databases
• extend orchestration contracts, projector/read-model, projection pipeline, websocket routing, and web store to support bulk imported messages / activities / proposed plans
• add explicit T3 import entry points in the sidebar and settings through a shared useLegacyT3Import flow
• fix desktop confirm usage so the import prompt uses the native bridge instead of falling back incorrectly in packaged builds
• add provider usage snapshots for Codex and Claude from local CLI/session data, then reuse the same summary in Rate limits remaining and the optional composer badge

Validation

• bun fmt
• bun lint
• bun typecheck

[Emanuele-web04]

@codex resolve the merge conflicts in this pull request

[chatgpt-codex-connector]

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