Phase 3 — Unify the Command Bus (UI + agent)

[ozgesolidkey]

Part of #14. Ref: docs/ARCHITECTURE_V2.md §3 (the key idea).

Define every capability ONCE as a typed command; IPC, localhost HTTP (agent), and in-process calls become transports over one CommandBus. The MCP server becomes a thin adapter.

Tasks

• Define shared/commands.ts typed command contract (doc.search, doc.getLines, analyze.run, triage.recipe, …).
• CommandBus + transports: ElectronIPC, HTTP, in-proc.
• Route renderer feature calls and api-server endpoints through the bus.
• Collapse duplicated handlers (e.g. trends exist in both main IPC and api-server today).
• MCP server re-expressed as a bus adapter.

Done when: one definition per capability; agent has automatic parity with the UI. (The triage recipe engine already previews this pattern.)