fix(desktop): disclose sticky model overrides

[embwl0x]

Summary

• keep a memory-only mirror of the profile default even when a sticky composer selection survives startup
• show a compact warning icon and explanatory tooltip when a new-chat composer model differs from Settings
• refresh the mirror immediately after Settings changes while leaving active-session model state unlabelled

Current-main proof

On d37090ac3, a persisted composer model makes refreshCurrentModel() return before getGlobalModelInfo(). The regression failed with:

expected getGlobalModelInfo to be called once, but got 0 times

The fixed path reads the profile default without clobbering the sticky selection, so the UI can disclose the override before session.create sends it.

Validation

• 42 affected Desktop model, session-store, menu, and localization tests passed
• focused ESLint passed
• npx tsc -b --pretty false passed
• full npm run build passed
• git diff --check passed
• publish gate and pushed-range gitleaks passed

Fixes #62055

[embwl0x]

Closing this branch to avoid parallel work with the earlier canonical implementation in #58527 and its CI-enabled replacement #62486.

Those branches correctly distinguish picker-originated state from stale/default-derived state. This PR's additional warning for an intentional manual override remains complementary, so I documented that tested invariant on #58527 for maintainers to retain if useful. I am not force-pushing the local conflict resolution around the duplicate-preflight block.