Fix provider and model selection drift between settings, drafts, and restored sessions #39
Description
Problem
The renderer maintains global settings, draft session defaults, and restored session metadata at the same time. In practice, the active model/provider can drift between those layers: a restored session may show one model while settings point to another, draft sessions may inherit stale provider state, and UI controls can appear to update globally even when a change should only apply to the next new session.
Why this matters
Provider drift causes hard-to-debug behavior. Users can believe they are testing Ollama when the runtime is still using OpenRouter, or think a restored session adopted new settings when it is still pinned to old metadata. This also makes bug reports around model choice and permission behavior much harder to triage.
Acceptance Criteria
- Active-session model/provider display should always match the actual runtime configuration for that session.
- Changing global settings should affect new drafts predictably without silently mutating existing live sessions.
- Restoring an older session should surface its effective model/provider clearly, even if current defaults have changed.
- Session resurrection after app restart should preserve the correct provider-specific fields.
- Include manual repro notes for at least: switching providers, restoring an old session, starting a new draft, and sending the first prompt.