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/shared/package.json

@@ -14,7 +14,9 @@
     "./src/activities": "./src/activities.ts",
     "./src/activities.js": "./src/activities.ts",
     "./src/constants": "./src/constants.ts",
-    "./src/constants.js": "./src/constants.ts"
+    "./src/constants.js": "./src/constants.ts",
+    "./src/audit": "./src/audit.ts",
+    "./src/audit.js": "./src/audit.ts"
   },
   "scripts": {
     "build": "tsc",

packages/shared/src/audit.ts

@@ -0,0 +1,44 @@
+/**
+ * Audit action vocabulary, shared so the server writes and the client renders
+ * the same strings. Values are stored in the database, so renaming one
+ * rewrites history — add new actions instead.
+ */
+export const AUDIT_ACTIONS = [
+  'space.update',
+  'space.transfer_ownership',
+  'channel.create',
+  'channel.update',
+  'channel.delete',
+  'member.kick',
+  'member.leave',
+  'member.ban',
+  'member.unban',
+  'role.create',
+  'role.update',
+  'role.delete',
+  'invite.create',
+  'message.delete',
+] as const;
+
+export type AuditAction = (typeof AUDIT_ACTIONS)[number];
+
+export interface AuditEventActor {
+  id: string;
+  username: string;
+  displayName: string | null;
+  avatar: string | null;
+}
+
+export interface AuditEvent {
+  id: string;
+  spaceId: string;
+  action: AuditAction;
+  actor: AuditEventActor | null;
+  targetType: string | null;
+  targetId: string | null;
+  /** Shape depends on `action`; used for display only. */
+  metadata: Record<string, unknown> | null;
+  createdAt: number;
+}
+
+export const AUDIT_PAGE_SIZE = 50;