feat: add platform key usage to mcp auth

TASKS.md

@@ -2,15 +2,14 @@
 
 ## Current
 
-### `feat/demo-assets`
+### `feat/platform-key-usage`
 
-Status: in_progress
+Status: completed
 
 DoD:
-- project has an idempotent PostgreSQL demo seed for live UI screens
-- demo seed fills workspaces, memberships, invitations, operations, agents, keys and usage
-- seed is controlled by env and does not live in migrations
-- docs explain how to enable and use demo data
+- platform API keys authenticate real machine access
+- `last_used_at` updates from successful platform key usage
+- UI API keys page reflects honest runtime usage rather than seed-only metadata
 
 ## Next
 
@@ -18,6 +17,4 @@ DoD:
 
 ## Backlog
 
-- `feat/current-workspace-session-model`
-- `feat/agent-lifecycle-polish`
-- `feat/platform-key-usage`
+- `feat/alpine-polish`