T-14: Unified application(_:open:) open-handler for external triggers

[kirich1409]

Part of EPIC #193. Depends on #194, #201.

Description

Implement application(_:open:) on AppDelegate to route external open triggers: folder drag onto the Dock icon, open -a Relay <path> from the terminal, and the relay://project?path=X URL scheme. For each URL, canonicalize → ProjectID → openWindow(value: projectID). Deduplication is then guaranteed by SwiftUI. URL scheme parsing is a basic placeholder (path extraction); full command support is deferred post-MVP.

Acceptance Criteria

• Dragging a folder onto the Dock icon opens the project window; if already open, activates the existing window
• open -a Relay ~/project from the terminal behaves identically
• relay://project?path=/path/to/project URL opens the project
• URL parse errors are logged, no crash
• Manual test: open a project via drag, then try to open it again via CLI — activates the existing window

Module / Layer

Relay / AppDelegate

Complexity

Medium