fix(combo): keep nested combos as single units and stop 0-token detail rows

Nested combos (comboA lists comboB, comboC, …) now stay one slot each:
the inner combo always runs as fallback to produce a single answer.
Failed hops are no longer written to Details/usage, and streaming no
longer inserts a 0-token placeholder row.

- chat.js: comboStack cycle detection; nested combos forced to fallback;
  persistUsage="success-only" for combo hops
- combo.js: discardResponse() cancels unused bodies (fusion timeout /
  fallback) so dropped streams fire onStreamComplete; getComboModelsFromData
  keeps nested names and honors enabled=false
- requestDetail.js: tokensForDetail() canonicalizes Claude/Gemini usage;
  shouldPersistRequestDetail() skips streaming-start and non-success hops
- streamingHandler.js: drop the 0-token streaming placeholder write
- RequestDetailsTab.js: read Gemini/Claude token names; show "streaming"
  status in amber
- tests: add combo-nested.test.js (13 cases)
- gitignore: ignore local .vitest/ artifacts

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>

CHANGELOG.md

@@ -7,6 +7,7 @@
 - **Providers**: wire the dead "Fetch Models" button on compatible nodes to the live upstream catalog, de-duplicating against already-added models
 
 ## Fixes
+- **Usage**: nested combos (comboA lists comboB, comboC, …) stay one slot each — the inner combo always runs as fallback to produce a single answer, failed hops are not written to Details/usage, and streaming no longer inserts a 0-token placeholder. One user message against a nested fallback combo is one request row with real tokens; fusion of nested combos is N panel slots + judge, not every nested leaf
 - **Models**: persist per-model capability assertions for custom and compatible providers and honor them everywhere — unsupported media is stripped on the chat path, `/v1/models` and `/api/models` report what the user asserted, and thinking translation follows it (asserting `reasoning:false` now actually strips thinking fields, `reasoning:true` emits them)
 - **Models**: partial capability edits merge instead of overwriting, so toggling vision off no longer erases a stored reasoning assertion
 - **Capabilities**: keep server-injected readers (synced catalog, user-asserted capabilities) in process-wide state — Next.js compiles startup and each API route into separate bundles with their own module instances, so a boot-time install was invisible to every request handler and the models.dev catalog contributed nothing to upstream requests since 0532f00d