Add public/private calendars, full iCal support, and iCal URL import

- Public/private: toggle is_public via PUT /calendars/{id}; generate/clear
  public_token and return ical_url when public
- Public feed: GET /cal/{token}/feed.ics (no auth) for subscription in
  Google/Apple/Outlook calendars
- Full iCal export: use golang-ical; VALARM, ATTENDEE, all-day (VALUE=DATE),
  RRULE, DTSTAMP, CREATED, LAST-MODIFIED
- Full iCal import: parse TZID, VALUE=DATE, VALARM, ATTENDEE, RRULE
- Import from URL: POST /calendars/import-url with calendar_id + url
- Migration: unique index on public_token, calendar_subscriptions table
- Config: BASE_URL for ical_url; Calendar model + API: ical_url field
- Docs: OpenAPI, llms.txt, README, SKILL.md, about/overview

Made-with: Cursor

internal/repository/models.go

@@ -58,6 +58,14 @@ type CalendarMember struct {
 	Role       string      `json:"role"`
 }
 
+type CalendarSubscription struct {
+	ID           pgtype.UUID        `json:"id"`
+	CalendarID   pgtype.UUID        `json:"calendar_id"`
+	SourceUrl    string             `json:"source_url"`
+	LastSyncedAt pgtype.Timestamptz `json:"last_synced_at"`
+	CreatedAt    pgtype.Timestamptz `json:"created_at"`
+}
+
 type Contact struct {
 	ID        pgtype.UUID        `json:"id"`
 	OwnerID   pgtype.UUID        `json:"owner_id"`