Show Codex account usage in Decodex App

[yvette-carlisle]

Summary

• add server-owned /api/accounts routes for cached Codex account usage and account mutations
• route Decodex App account list/select/clear/logout/import/use through decodex serve, with helper retained only for streamed account_login
• reuse an existing local decodex serve instead of starting duplicates; if no server is present, start the bundled decodex serve --api-only so App-owned servers do not poll Linear or dispatch work
• remove the generic helper fallback for account commands: non-login account operations must be served by the server
• show plan plus 5h / 7d remaining usage chips and preload account state so the first menu click is not empty
• package and sign the bundled decodex server binary alongside decodex-app-helper

Verification

• cargo make check-rust
• cargo make check-vstyle-rust
• cargo test -p decodex api_only -- --nocapture
• cargo test -p decodex operator_state_endpoint_serves_account_api_snapshot -- --nocapture
• cargo test -p decodex list_response_merges_usage_snapshot -- --nocapture
• swift build --package-path apps/decodex-app
• cargo make test-decodex-app-stage
• ./apps/decodex-app/script/build_and_run.sh --verify
• git diff --check

Operational Notes

• Rebased onto origin/main at 32d83fab.
• Existing full decodex serve instances remain the source of truth for App/WebUI state.
• App-started servers are API-only and publish automation_disabled; they do not tick registered projects or touch Linear queues.
• On this machine, the App was restarted and reused the already-running 127.0.0.1:8912 pubfi server instead of starting another server.