feat(extensions): accept Claude command permission hints

[limityan]

Summary

• accept Claude legacy Command allowed-tools in its documented string and YAML list forms
• validate the hint without projecting it into BitFun command contracts, behavior versions, or permission grants
• keep malformed metadata fail-closed and preserve restrictions for disallowed-tools and other unsupported behavior fields
• document the adapter and permission-owner boundary in the existing external-source architecture guide

Type and Areas

Type: Feature

Areas: Rust adapters, external extension compatibility, architecture docs

Motivation / Impact

Claude Code uses allowed-tools as a permission preapproval hint rather than a restrictive tool allowlist. BitFun previously treated the field as an unsupported execution capability, which unnecessarily restricted otherwise compatible legacy Commands.

Supported Commands can now load while every tool invocation continues through BitFun's existing permission and safety policies. Invalid field types still invalidate the source file, and no external hint can grant preapproval.

Verification

• cargo test -p bitfun-claude-code-adapter: 55 passed
• cargo check --workspace: passed; existing unrelated warnings only
• pnpm run check:repo-hygiene: passed
• git diff --check: passed
• independent adversarial review: no remaining P0/P1/P2/P3 findings

Reviewer Notes

• No public DTO, event, runtime port, permission layer, dependency, or UI changes.
• allowed-tools does not participate in the command behavior version because it does not change BitFun execution behavior.
• Plugin Host Runtime, LSP, plugin discovery, and scoped permission leases remain out of scope.
• Implementation and review were AI-assisted; validation level: fully tested.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.