fix(desktop): scope sidebar messaging and cron caches by profile

[kim-miram]

Summary

• scope sidebar backend, Electron, and legacy fallback reads to the active profile
• keep explicit all-profile mode separate while preventing cross-profile messaging and cron cache writes
• guard stale pagination, cron mutations, and same-named-profile gateway-switch responses with scope/generation/epoch tokens

Test plan

• npm --workspace apps/desktop test — 4,634 passed, 2 skipped
• npm --workspace apps/desktop run typecheck
• npm --workspace apps/desktop run lint — 0 errors
• uv run --extra dev pytest tests/hermes_cli/test_web_server.py::TestWebServerEndpoints -q — 57 passed
• Added regression coverage for concrete-profile isolation, stale response ordering, and gateway invalidation

No credentials, user data, profiles, or transcripts are included.

[alt-glitch]

This was generated by AI during triage.

Related to #70630 and #70629: this addresses the same Desktop concrete-profile sidebar boundary, with additional cache and stale-response handling. Maintainer review should select or consolidate the overlapping implementations.

[teknium1]

Substantial overlap with work now on main: fetch scoping + stale-pagination guards landed via #87566, and the gateway-switch serialization via #87600. What survives here: cron store cache scoping (store/cron.ts), the Electron/legacy-fallback backend scoping halves, and the same-named-profile epoch tokens. Leaving open — a rebase would isolate the surviving parts.