fix: restore long-running sessions reliably

[jarynclouatre]

Summary

• persist active Claude and Codex sessions across Bridge restarts and restore them lazily
• bound and deduplicate Codex history loading so large sessions do not exhaust Bridge memory
• suppress false Working state while restored history is loading and improve real activity feedback
• preserve queued Codex input and session settings through process exits and mode restarts

Verification

• TypeScript typecheck passed
• 368 focused Bridge tests passed; final websocket suite passed 174/174
• 134 focused Flutter tests passed
• no emulator/E2E tests were run