fix(documents): source the condition chips from the usage endpoint

The filter bar derived its condition chips from the loaded corpus, so an
episode whose only linked documents sat pages deep in the timeline never
surfaced a chip — the condition route into an older document silently
disappeared at four-digit corpus sizes. The usage endpoint (already read
on page mount) now returns `linkedEpisodes` — every episode carrying at
least one live document link, one indexed grouped query, no blobs — and
the view unions it with the active-filter fallback. Additive DTO change;
OpenAPI regenerated.

docs/api/openapi.yaml

@@ -8851,8 +8851,8 @@ paths:
       summary: Storage usage + effective limits
       description: "The caller's vault usage and effective limits: `usedBytes` (every non-purged row — tombstones inside the
         30-day undo grace still count), `quotaBytes` (per-user override ?? instance default), `maxFileBytes`
-        (admin-tunable per-file cap), and `acceptedExtensions` for picker `accept` lists. Read this before offering an
-        upload."
+        (admin-tunable per-file cap), `acceptedExtensions` for picker `accept` lists, and `linkedEpisodes` (episodes
+        carrying at least one live document link — the condition-filter chips). Read this before offering an upload."
       responses:
         "200":
           description: Usage + limits.
@@ -26021,11 +26021,25 @@ components:
           type: array
           items:
             type: string
+        linkedEpisodes:
+          type: array
+          items:
+            type: object
+            properties:
+              episodeId:
+                type: string
+              name:
+                type: string
+            required:
+              - episodeId
+              - name
+            additionalProperties: false
       required:
         - usedBytes
         - quotaBytes
         - maxFileBytes
         - acceptedExtensions
+        - linkedEpisodes
       additionalProperties: false
     DocumentBulkEnvelope:
       type: object