Ship a Logbuch skill and record token use

- docs/skill.md teaches a Claude what Logbuch is for, how an entry sounds
  and in which order the calls go, served at GET /api/v1/skill and as a
  download next to the spec and the guide
- a test keeps the skill from drifting: frontmatter, only endpoints that
  exist, house rules
- resolveClient stamps last_used_at, the access list said never used even
  after eleven entries

src/lib/api-auth.ts

@@ -1,5 +1,5 @@
 import { createHash } from 'node:crypto'
-import { findActiveClientByTokenHash } from '~/data/repositories/clients'
+import { findActiveClientByTokenHash, markClientUsed } from '~/data/repositories/clients'
 import type { ApiClient } from '~/data/schema'
 
 export function hashToken(token: string): string {
@@ -19,5 +19,11 @@ export async function resolveClient(request: Request): Promise<ApiClient | undef
 		return undefined
 	}
 
-	return findActiveClientByTokenHash(hashToken(token))
+	const client = await findActiveClientByTokenHash(hashToken(token))
+
+	if (client) {
+		await markClientUsed(client.id)
+	}
+
+	return client
 }