Fix home-folder chat stall during instruction discovery

[AetherAI3]

Summary

• Bound nested AGENTS.md discovery by directory count, entry count, and elapsed time before a chat turn starts.
• Preserve direct project and user instructions and show an explicit warning when nested discovery is incomplete.
• Refuse local tool authority when nested rules could be missing; hosted cloud chat may continue with a visible warning.

Reproduction and validation

The published 0.3.2 CLI launched from C:\Users\lilbe echoed just testing reply 1 and produced no pulse or response after more than 30 seconds. The same CLI in a small project directory returned a terminal response promptly. The delay was the synchronous nested instruction walk before the network request.

With this branch, discovery from the same home folder completes in about 60 ms with an explicit incomplete marker. A built 0.4.0 CLI launched from that folder displays the warning and reaches a terminal cloud response in about 1.7 seconds with a synthetic invalid key; this test makes no model call. Direct project and user instructions remain loaded. A valid account can then proceed through the normal hosted turn.

Checks: npm run build; 78 focused tests across chat, instruction resolver, and skill host loop passed with the package's --test-isolation=none setting. The new wide-directory test exercises warning and local refusal.

The synchronous readdirSync of one directory remains a single filesystem operation that cannot be preempted by this budget; the result is checked before sorting or statting its entries.