feat(tokens): mint a workouts:write token for headless workout ingest

A bridge that pushes workouts from a watch vendor had no credential that
reached POST /api/workouts/batch: the route called requireAuth() with no
scope, so under the fail-closed default only a cookie session or a
wildcard token got through, and a measurements:write token was refused
403. The route's header still described the pre-fail-closed behaviour.

Add a separate workouts:write scope rather than widening
measurements:write, so a token already handed to a scale does not start
accepting workouts.

- POST /api/tokens/workouts mints it, mirroring the measurement and
  document mints: cookie session plus a fresh proof, a literal permission
  array, 10 mints a minute, at most 10 live tokens (409
  tokens.workouts.ceiling_reached), a one-year default lifetime, audited.
- POST /api/workouts/batch names the scope. Sessions and wildcard tokens
  behave as before. A scoped caller's workouts are stored as EXTERNAL,
  resolved from the credential, and a batch in which any entry names a
  source is refused 422 (workout.batch.source_not_permitted), the same
  rule the measurement batch applies. EXTERNAL is on no source ladder, so
  when the phone recorded the same session the phone's copy is shown.
- Settings > API offers a workout token card next to the measurement one,
  and the endpoint list shows the batch route.
- Guards: the mint site, the declared scope vocabulary, the recent-proof
  routes, and a new check that only the batch declares the scope.
- OpenAPI documents the mint, the batch's narrow-token behaviour and both
  error codes; docs/api/README.md lists the workout and document mints.

Refs #1054

src/components/settings/security-section/__tests__/recent-proof-callers.test.tsx

@@ -71,6 +71,8 @@ describe.each([
   ["components/settings/share-link-create-form.tsx", "/api/share-links"],
   ["components/settings/mcp-section.tsx", "/api/mcp/tokens"],
   ["components/settings/api-section.tsx", "/api/tokens/measurements"],
+  ["components/settings/api-section.tsx", "/api/tokens/documents"],
+  ["components/settings/api-section.tsx", "/api/tokens/workouts"],
   ["components/admin/backups-section.tsx", "/download"],
   ["components/admin/backups-section.tsx", "/restore"],
   ["components/admin/backups-section.tsx", "/api/admin/backups/upload"],