feat(desktop): channel templates — reusable project settings

[wesbillman]

Summary

• Channel templates that pre-configure channel type, visibility, canvas content, and agent roster — managed in Settings → Channel Templates
• Async agent startup: after creating a channel from a template, navigation is instant — agents spin up in the background via fire-and-forget Promise.allSettled (parallel, not sequential)
• Extracted useApplyTemplate hook: template canvas + agent apply logic pulled out of AppShell into a dedicated hook, reducing AppShell by ~150 lines
• Rust backend: local JSON storage for templates with full CRUD via Tauri IPC

Details

• Apply flow: create channel → set canvas → navigate → (background) create agents → invalidate caches → toast on failures
• Provider/model resolution: template entry → persona default → user runtime default (first non-null wins)
• Partial agent failures show a toast warning; agent creation never blocks navigation or the dialog
• Cache invalidation after background agent creation ensures members sidebar updates immediately
• Direct-persona dedup prevents duplicate agents when a persona appears in both direct entries and team expansions

NITs noted during review (not addressed)

• Cache invalidation in useApplyTemplate uses string literals instead of exported query key constants
• Theoretical stale-closure if persona/provider queries haven't resolved when user submits (unreachable in practice — Tauri queries resolve in ms)

Test plan

• Create a template in Settings → Channel Templates with personas and teams
• Create a channel using the template — verify instant navigation, agents appear within seconds
• Create a template with invalid persona IDs — verify toast warning on partial failures
• Create a channel without a template — verify no behavioral change
• Edit, duplicate, and delete templates in settings

🤖 Generated with Claude Code

[wesbillman]