feat: add OpenCode Go usage query with aggregated /all endpoint, bump v0.3.0

- New provider: OpenCode Go (GET https://opencode.ai/zen/go/v1/usage, Bearer auth)
- Extract shared transport doUpstreamRequest (host.http.do first, net/http fallback)
- New management routes: GET/POST /plugins/commandcode/opencode/usage, GET/POST /plugins/commandcode/all
- /all aggregates both providers sequentially with partial-failure semantics
  (>=1 success -> 200, all-local-missing -> 400, all-upstream-failure -> 502)
- QuotaCard UI: tabs (Command Code / OpenCode Go / All), OpenCode window cards,
  version badge v0.3.0, OpenCode API key test override in settings drawer
- Config: opencode_api_key / opencode_api_base (ConfigFields 2 -> 4)
- Tests: route-order regression, /all partial failure & misclassification guards,
  ParseOpenCodeUsage edge cases, host/http transport paths

.gitignore

@@ -20,3 +20,6 @@ coverage.txt
 *.zip
 checksums.txt
 dist/
+
+# Internal planning docs (not for public repo)
+docs/