feat(runtime): harden delegation and collaboration trust boundaries

[ozereray]

Aegisora 2.0 enterprise authority hardening

This release closes the multi-agent trust boundary around delegated execution and collaboration.

Security

• Delegation capabilities are identity-bound.
• Parent/child identities cannot be forged or swapped.
• Tool and provider scopes are enforced.
• Expiry and revocation are enforced.
• Sibling capability isolation is enforced.
• Collaboration task ownership is enforced.
• Completed tasks cannot be replayed.
• Delegation authority remains internal to runtime governance.

Verification

• Runtime build: PASS
• Runtime regression: 85 tests PASS
• Delegation traces 101-107: PASS
• Collaboration traces 113-114: PASS
• Evidence traces 115-116: PASS
• Worktree clean
• Commit: a290d32