Show catalog load failure as an error, not an empty picker (CL-6831)

[TheGreatAxios]

Summary

A failed resolved-catalog load on the workbench-settings agent model picker used to look like an empty dropdown: CatalogState error had no message, the select stayed enabled, and the empty-ready hint only rendered for kind === "ready". The catch now stores describeChatError copy, disables the select, and offers Retry plus a Shared Settings hop. It does not reuse the empty-catalog "No connected providers yet" string.

Verification

• cd packages/chat-ui && bun test test/agents-section.test.tsx: new catalog-failure cases failed before the implementation (select still enabled), then 23 pass, 0 fail (exit 0) after.
• cd packages/chat-ui && bun test test/agents-section.test.tsx src/workbench-settings/agents-section.test.ts: 30 pass, 0 fail (exit 0).
• bun run typecheck: exit 0.
• bun run lint: prettier clean; eslint 0 errors / 10 pre-existing warnings.
• bunx eslint --cache packages/chat-ui/src/workbench-settings/agents-section.tsx packages/chat-ui/src/strings.ts packages/chat-ui/test/agents-section.test.tsx: exit 0.
• Full bun run check / bun run test reach scripts/db-setup.test.ts and fail with PostgresError: password authentication failed for user "thegreataxios" (pre-existing local DATABASE_URL, unrelated).

Fixes CL-6831

[linear-code]

CL-6831

[TheGreatAxios]

Self-review

Verdict: the fix is correct — describeChatError now recognizes InferenceSettingsApiError, surfaces its safe userMessage on unmapped statuses, the select disables on kind: "error", and Retry/Shared-Settings actions are wired through a reload key. No defects found; nothing changed.

• describeChatError's 401/403/undefined-status mapping and InferenceSettingsApiError handling: DISMISSED — verified against InferenceSettingsApiError (packages/inference-settings/src/api.ts), whose message is always the parsed envelope's userMessage (safe to show) or a generic "server answered N" string, never a raw path; the ChatApiError 500 case still returns the generic fallback, so no regression there.
• /settings/connections hop target: DISMISSED — matches the existing route (packages/settings-ui/src/connections-section.tsx, packages/connections/src/oauth-routes.ts), not a fabricated path.
• Retry wiring (catalogReloadKey in the effect deps, resetting to loading on each run): DISMISSED — re-read the effect; it cancels the prior run via the cancelled closure and correctly clears the previous error/models on retry.
• CatalogState exhaustiveness / ModelSelect disabled + hint conditions after adding the error variant: DISMISSED — typecheck passes, no orphaned branches.

Targeted tests (from packages/chat-ui, in the PR's worktree): bun test test/agents-section.test.tsx test/api.test.ts src/workbench-settings/agents-section.test.ts → 73 pass, 0 fail. bun run typecheck → exit 0.