🤖 feat: add default-hidden Daybreak models - #4113

Summary

Add openai:daybreak-blue-latest and openai:daybreak-red-latest to the known models, hidden by default and available to enable independently in Settings.

Seed visibility once so later enable/disable choices survive reloads. Preserve existing defaults, legacy local-only preferences, and same-tab or cross-tab changes made while startup config is loading. Persist migrations without delaying settings hydration. ACP model options honor the same visibility preferences while retaining the current selection. Update the model reference and generated built-in docs.

Validation

• make static-check passed.
• Focused suites passed: known models, backend config, model settings hook, local preference migration, and WorkspaceContext.
• 114 non-live ACP and model-preference IPC tests passed, covering visibility choices, current-selection retention, and persistence.
• Red-green regression coverage covers failed or stalled migration writes, malformed persisted visibility, and edits made before startup config resolves. Tests also verify cross-tab writes before their storage events arrive, toggling back to the original value, per-field migration, and backend authority after reconnect.
• Live ACP API tests were blocked by the missing ANTHROPIC_API_KEY. Remote UAT was not run: no agent-enabled Coder template for coder/xum was available.

Risk

The startup migration changes preference synchronization. It preserves edits made during the current client's startup and keeps unrelated settings hydration independent of persistence. Separate clients still use the existing last-write-wins preference API.