refactor(agent-package): index archive path admission

[Yevanchen]

Summary

• Indexed agent package archive ancestor paths so descendant collision checks no longer scan every previously admitted path.
• Precomputed declared skill asset roots and check path prefixes by segment during package archive admission.
• Added archive admission tests for nested skill assets and root-path rejection.

Why

• The complexity optimizer scan flagged archive path admission as a repeated-scan hotspot. Large package archives could re-scan prior entries and declared skill roots per path even though the checks only need prefix membership.

Closes YEF-910

Verification

• Commands:
  • bun test pkgs/agent-package/tests/archive-entry-admission.test.ts
  • bun run --filter @mosoo/agent-package test
  • bun run --filter @mosoo/agent-package tc
  • bun run --filter @mosoo/agent-package lint
  • just fmt-check-path pkgs/agent-package/src/archive-entry-admission.ts
  • just fmt-check-path pkgs/agent-package/src/archive-path-policy.ts
  • just fmt-check-path pkgs/agent-package/tests/archive-entry-admission.test.ts
  • git diff --check
  • just commit-check
  • just check (blocked by unrelated apps/driver/tests/acp-file-system.test.ts path assertion: expected /tmp/..., received /private/tmp/... on this macOS workspace)
• Manual steps: N/A
• Not run: N/A

Impact

• User/API/contract changes: None.
• Generated files / GraphQL / DB / lockfile: None.
• Env or config changes: None.
• Risk and rollback: Low; path admission semantics are covered by existing and new archive parser tests. Roll back commit 16231b11 if needed.

Review

• Closest review areas: pkgs/agent-package/src/archive-entry-admission.ts, pkgs/agent-package/src/archive-path-policy.ts.
• Known trade-offs: The full repo gate still needs the unrelated driver temp-path assertion fixed or normalized for macOS /private/tmp workspaces.