feat(core,fuse,gui): show a sync issue on its node in the file browser

A refused change was only on the Sync page. A folder listing now carries
each node's issue (by local id, so a file not yet on Drive has it too),
and the browser's badge ranks it first, folders included, with the
issue's explanation as its tooltip. The event sampler publishes Files
when the set of issues changes, so the badge comes and goes with it.

docs/MILESTONE-3.0.0-STATUS.md

@@ -12,7 +12,7 @@ Tracks `docs/MILESTONE-3.0.0.md`. Update it with every commit that moves a phase
 - Fixes from the simulation and account runs since then: B125, B127, B130 and B141 to B181.
 - **Sync issues, first cut** (§6.2): refusals sorted into issues, shown at once in the app,
   tray and CLI; Export button and `pdfs sync export`; `pdfs sync issues`; Discard button and
-  `pdfs sync discard`.
+  `pdfs sync discard`; a warning badge on the node in the file browser.
 
 ## Phase 3: left for 3.0.0
 
@@ -32,8 +32,9 @@ Tracks `docs/MILESTONE-3.0.0.md`. Update it with every commit that moves a phase
          undo the local change it stood for: a node made here goes, a node Drive has goes back
          to what Drive has. Control request, `pdfs sync discard`, Discard button with a
          confirmation; translated in every catalog.
-   - [ ] Show the issue on the node itself (file browser emblem or status). Not in the first
-         cut.
+   - [x] Show the issue on the node itself: a folder listing carries each node's issue, and
+         the file browser shows a warning badge with what it means. The listing is published
+         again when the set of issues changes.
 2. **Planner and executor (§5.4, §5.5)**: ops keyed by local id; remove `mint_local_uid`,
    `finish_create` and `adopt_real_uid`; a landing create sets `remote_uid` on its row.
    - [x] Queued ops carry `lid` and `parent_lid` (schema 39). The claim reads the parent's uid