feat(store): add DeleteUser with cascading account deletion

backend/internal/store/schema.sql

@@ -26,7 +26,7 @@ CREATE TABLE users (
 -- below) in one transaction when a new account signs up.
 CREATE TABLE profile (
     id                  INTEGER PRIMARY KEY AUTOINCREMENT,
-    user_id             INTEGER NOT NULL REFERENCES users(id),
+    user_id             INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
     name                TEXT NOT NULL DEFAULT 'Default',
     garmin_email        TEXT NOT NULL DEFAULT '',
     garmin_password     TEXT NOT NULL DEFAULT '',
@@ -82,7 +82,7 @@ CREATE TABLE profile (
 -- recursive AND/OR condition tree evaluated by internal/classify.
 CREATE TABLE workout_kinds (
     id          INTEGER PRIMARY KEY AUTOINCREMENT,
-    user_id     INTEGER NOT NULL REFERENCES users(id),
+    user_id     INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
     name        TEXT NOT NULL,
     description TEXT NOT NULL DEFAULT '',
     color       TEXT NOT NULL DEFAULT '',
@@ -100,7 +100,7 @@ CREATE TABLE workout_kinds (
 -- synced activity log is the history. No user_id column of its own --
 -- ownership is checked via a JOIN to workout_kinds.
 CREATE TABLE workout_type_paces (
-    workout_kind_id     INTEGER PRIMARY KEY REFERENCES workout_kinds(id),
+    workout_kind_id     INTEGER PRIMARY KEY REFERENCES workout_kinds(id) ON DELETE CASCADE,
     pace_min_sec_per_km REAL,
     pace_max_sec_per_km REAL,
     hr_min_pct_hrr      REAL,
@@ -118,7 +118,7 @@ CREATE TABLE workout_type_paces (
 -- instead of storing a redundant copy.
 CREATE TABLE activities (
     id                         INTEGER PRIMARY KEY AUTOINCREMENT,
-    user_id                    INTEGER NOT NULL REFERENCES users(id),
+    user_id                    INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
     garmin_activity_id         INTEGER NOT NULL,
     -- Derived at sync time from Garmin's own eventType.typeKey=="race" --
     -- a hard fact, not a rule the user tunes (see internal/classify's
@@ -219,7 +219,7 @@ JOIN (
 -- re-walking years of already-known history on every call.
 CREATE TABLE sync_state (
     id                   INTEGER PRIMARY KEY AUTOINCREMENT,
-    user_id              INTEGER NOT NULL REFERENCES users(id),
+    user_id              INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
     earliest_synced_date TEXT,
     backfill_complete    INTEGER NOT NULL DEFAULT 0,
     UNIQUE(user_id)
@@ -229,7 +229,7 @@ CREATE TABLE sync_state (
 -- status the frontend polls.
 CREATE TABLE sync_runs (
     id                 INTEGER PRIMARY KEY AUTOINCREMENT,
-    user_id            INTEGER NOT NULL REFERENCES users(id),
+    user_id            INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
     kind               TEXT NOT NULL CHECK(kind IN ('backfill','incremental','full')),
     started_at         TEXT NOT NULL,
     finished_at        TEXT,