fix(delegate-task): remove kimi from unstable agent detection, harden callID resolution for metadata store

- Remove kimi from auto-detected unstable agents in category-resolver (only gemini/minimax remain)
- Add resolveCallID() to safely resolve callID/callId/call_id variants from tool context
- Use resolveCallID across all 5 delegate task execution paths (sync, background, unstable, continuations)
- Update writing category test to verify kimi runs sync when kimi provider is available
- Add atlas metadata preservation tests confirming tool-execute-after does not clobber metadata

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

src/tools/delegate-task/resolve-call-id.ts

@@ -0,0 +1,5 @@
+import type { ToolContextWithMetadata } from "./types"
+
+export function resolveCallID(ctx: ToolContextWithMetadata): string | undefined {
+  return ctx.callID ?? ctx.callId ?? ctx.call_id
+}