lift restriction on object_id and UID having to match

addresses #135

crates/store_sqlite/migrations/20251101181540_add_calendar_uid.up.sql

@@ -0,0 +1,53 @@
+-- Adds the column "uid" and populates it with data from "id"
+ALTER TABLE calendarobjects RENAME TO calendarobjects_old;
+
+CREATE TABLE calendarobjects (
+    principal TEXT NOT NULL,
+    cal_id TEXT NOT NULL,
+    id TEXT NOT NULL, -- filename
+    "uid" TEXT NOT NULL, -- global identifier
+    ics TEXT NOT NULL,
+    updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+    deleted_at DATETIME,
+
+    -- For more efficient calendar-queries
+    first_occurence DATE,
+    last_occurence DATE,
+    etag TEXT,
+    object_type INTEGER NOT NULL,  -- VEVENT(0)/VTODO(1)/VJOURNAL(2)
+
+    CONSTRAINT pk_calendarobject_id PRIMARY KEY (principal, cal_id, id),
+    CONSTRAINT uq_calendarobject_uid UNIQUE (principal, cal_id, "uid"),
+    CONSTRAINT fk_calendarobject_calendar FOREIGN KEY (principal, cal_id)
+    REFERENCES calendars (principal, id) ON DELETE CASCADE
+);
+
+CREATE INDEX idx_calobjs_uid ON calendarobjects (principal, cal_id, "uid");
+
+INSERT INTO calendarobjects (
+    principal,
+    cal_id,
+    id,
+    "uid",
+    ics,
+    updated_at,
+    deleted_at,
+    first_occurence,
+    last_occurence,
+    etag,
+    object_type
+) SELECT
+    principal,
+    cal_id,
+    id,
+    id AS "uid",
+    ics,
+    updated_at,
+    deleted_at,
+    first_occurence,
+    last_occurence,
+    etag,
+    object_type
+FROM calendarobjects_old;
+
+DROP TABLE calendarobjects_old;