# [FEATURE] Add Google Calendar support

## Description
Add Google Calendar support.

## User Story
As a user, I want my Google Calendar events displayed so I have a unified daily view.

## Technical Context
- New integration following existing patterns in `internal/api/`
- OAuth2 flow required; store refresh token in `sync_tokens` table
- New partial for calendar events display

## Test Strategy

### Unit Test (Red)
**File:** `internal/api/gcal_test.go`

```go
func TestParseCalendarEvents(t *testing.T) {
    // Mock Google Calendar API response
    // Assert events parsed correctly with title, time, all-day flag
}

func TestGCalClient_FetchEvents(t *testing.T) {
    // Mock HTTP client
    // Assert correct API calls made
    // Assert events returned in expected format
}
```

### Integration Test (Red)
Test cache/store roundtrip for events.

```go
func TestGCalEventsCache(t *testing.T) {
    // Store events in cache
    // Retrieve from cache
    // Assert data integrity
}
```

## Proposed Approach

1. **OAuth Setup:**
   - Add `GOOGLE_CLIENT_ID`, `GOOGLE_CLIENT_SECRET` to config
   - Implement OAuth2 flow with PKCE
   - Store refresh token in `sync_tokens` table

2. **API Client:**
   - Create `internal/api/gcal.go` implementing interface pattern from existing clients
   - Use `google.golang.org/api/calendar/v3`
   - Fetch events for configurable date range (default: today + 7 days)

3. **Data Model:**
   - Add `calendar_events` table or reuse existing structure
   - Handle all-day vs timed events

4. **UI:**
   - New partial: `partials/gcal-events.html`
   - Integrate into existing tabs or new calendar tab

## Traps to Avoid
- **All-day events:** Google returns these differently (date vs dateTime)
- **Timezone:** Events have their own timezone; convert to user's local
- **Recurring events:** Decide whether to expand or show as single item
- **Token refresh:** Handle expired access tokens gracefully

## Affected Components
- `internal/api/gcal.go` (new)
- `internal/api/gcal_test.go` (new)
- `internal/api/interfaces.go` (add interface)
- `internal/config/config.go`
- `internal/store/sqlite.go` (new table/queries)
- `web/templates/partials/gcal-events.html` (new)
- `cmd/dashboard/main.go` (wire up client)

## Definition of Done
- [ ] OAuth2 flow authenticates with Google
- [ ] Events fetched from Google Calendar API
- [ ] Events cached in SQLite
- [ ] Events displayed in UI
- [ ] All-day and timed events handled correctly
- [ ] Token refresh works
- [ ] Unit and integration tests pass