feat(audit): append-only audit log for spaces

Records who changed what, and is the mechanism statistics will read — one
event table rather than two logs that drift apart.

The table is deliberately generic (action + target + JSON metadata) so a new
action needs no migration. Writes never throw: a kick must not fail because
its log entry could not be written, since the kick already happened.

Leaving is recorded as a different action from being removed. The same route
serves both, and a log that conflates them misleads exactly when it matters.

Actor is nullable with ON DELETE SET NULL: the event outlives the account, and
a log that vanished with its actor would be worthless. Reads are gated on
MANAGE_SPACE rather than a new permission bit, which would default to nobody
until every role was re-edited. Paging uses the snowflake id, stable even for
two events in the same millisecond, and an action this build does not know
still renders a row.

packages/server/src/db/schema.ts

@@ -587,3 +587,26 @@ export const gifFavorites = sqliteTable('gif_favorites', {
   pk: primaryKey({ columns: [table.userId, table.gifId] }),
   userIdx: index('idx_gif_favorites_user_id').on(table.userId),
 }));
+
+/**
+ * Append-only record of who changed what in a space.
+ *
+ * Deliberately generic (action + target + JSON metadata) rather than a column
+ * per event type: new actions must not require a migration. Statistics read
+ * this same table — two features, one mechanism, instead of two logs that
+ * drift apart.
+ */
+export const auditEvents = sqliteTable('audit_events', {
+  id: text('id').primaryKey(),
+  spaceId: text('space_id').notNull().references(() => spaces.id, { onDelete: 'cascade' }),
+  actorId: text('actor_id').references(() => users.id, { onDelete: 'set null' }),
+  action: text('action').notNull(),
+  targetType: text('target_type'),
+  targetId: text('target_id'),
+  // JSON blob; shape depends on `action`. Never trusted for permissions.
+  metadata: text('metadata'),
+  createdAt: integer('created_at').notNull(),
+}, (table) => ({
+  spaceIdx: index('idx_audit_events_space_created').on(table.spaceId, table.createdAt),
+  actorIdx: index('idx_audit_events_actor').on(table.actorId),
+}));