Summary:

- Allow agent tool-call locations outside visible worktrees to resolve
as local buffers.
- Fall back to opening absolute paths from the tool-call click handler.

Tests:

- cargo test -p acp_thread
test_tool_call_location_resolves_external_file
- cargo check -p agent_ui

Closes AI-362
Release Notes:

- Fixed opening agent-created files outside the current project, such as
global skill files.