Complete Wave 2 handshake and Windows CI fixes

[ericmichael]

What changed

• perform the OmniAgents GUI initialize/initialized handshake before the desktop reports an RPC connection as ready
• repeat negotiation on reconnect and advertise the complete filesystem/git experimental surface
• narrowly retry when an older runtime explicitly rejects named experimental operations
• sync the generated GUI protocol artifacts to OmniAgents ba57696e
• replace repeated on-disk migration setup in projects-db tests with shared in-memory fixtures and isolated cleanup

Why

The desktop previously opened the WebSocket without completing the server-required GUI handshake, leaving filesystem/git RPC unavailable. Separately, Windows CI repeatedly exceeded Vitest's per-test budget because every migration test recreated an on-disk database and replayed all migrations.

Validation

• 35/35 targeted RPC client and lifecycle tests
• live isolated omni serve proof: initialize → initialized → fs_stat, all 31 fs/git operations negotiated
• 20 repeated projects-db runs: 440/440 passed; full suite: 55 passed, 11 skipped
• mutation proof confirmed a deliberately broken v15 migration still fails
• TypeScript typecheck, targeted ESLint/Prettier, protocol freshness/source verification, and 16/16 protocol-sync fixture tests

Tickets: tkt_PnOfb7dcQTfn, tkt_nfwUoeMve6cq