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

sqlc/queries/calendars.sql

@@ -31,3 +31,13 @@ WHERE id = $1 AND deleted_at IS NULL;
 -- name: SoftDeleteCalendarsByOwner :exec
 UPDATE calendars SET deleted_at = now(), updated_at = now()
 WHERE owner_id = $1 AND deleted_at IS NULL;
+
+-- name: GetCalendarByPublicToken :one
+SELECT id, owner_id, name, color, is_public, public_token, created_at, updated_at
+FROM calendars
+WHERE public_token = $1 AND is_public = true AND deleted_at IS NULL;
+
+-- name: SetCalendarPublicToken :exec
+UPDATE calendars
+SET public_token = $2, updated_at = now()
+WHERE id = $1 AND deleted_at IS NULL;

sqlc/queries/subscriptions.sql

@@ -0,0 +1,8 @@
+-- name: CreateCalendarSubscription :one
+INSERT INTO calendar_subscriptions (id, calendar_id, source_url)
+VALUES ($1, $2, $3)
+RETURNING *;
+
+-- name: GetSubscriptionByCalendar :one
+SELECT * FROM calendar_subscriptions
+WHERE calendar_id = $1;