feat(cu): add desktop presentation lifecycle

[hqhq1025]

Goal

Add the Desktop Computer Use presentation lifecycle as a reviewable layer above verified targeting and dispatch.

What this PR does

• adds a focusless, click-through, transparent agent-cursor BrowserWindow
• builds the overlay renderer and receive-mostly preload in normal build/dev flows
• maps only Runtime-bound observation coordinates into screen presentation coordinates
• waits up to 1 second for readyForInteraction, then fails open into native dispatch
• never waits for visual finished before returning the tool result
• commits visual completion only after Runtime accepts the post-dispatch lease and fresh observation
• cancels presentation for failed, stale, intervened, aborted, or otherwise discarded results
• validates mouse_move against the bound window and returns an executor-resolved completion point without injecting native pointer input
• serializes operations through the single visual cursor while keeping no-overlay session execution independent
• immediately releases active and queued presentation waits on session clear
• binds renderer acknowledgements to session, action, BrowserWindow generation, and current window identity
• tears down on load failure, renderer loss, display-layout change, session terminal boundaries, main-window close, and app shutdown
• supports the union bounds of multiple displays, including negative origins

Reverse-engineering constraints applied

The implementation follows the local Codex Computer Use lab findings:

• presentation identity is late-bound and is not execution evidence
• the visible completion coordinate comes only from executor resolvedScreenPoint
• presentation readiness is bounded and cannot redefine the execution target
• intervention/stale/stop states discard the result and must not show a success pulse
• stale renderer acknowledgements cannot settle a new operation
• the overlay cannot take focus or receive mouse input

Non-goals

• provider-specific Computer Use adapters or model loops
• physical-input, lock/unlock, blocked-URL, or service-loss event producers
• deterministic cumulative Electron E2E
• release packaging/signing/notarization
• Headless presentation support

Verification

• npm --workspace @maka/runtime test — full suite passed
• Runtime focused Computer Use tests — 47 passed
• npm --workspace @maka/computer-use test — 103 passed
• npm --workspace @maka/desktop run typecheck
• npm --workspace @maka/desktop test — 2419 passed
• npm --workspace @maka/desktop run build
• overlay controller/preload focused tests — 16 passed
• git diff --check

Real Electron smoke boundary

An earlier protocol revision produced a visible nonblank cursor screenshot. After adding session+generation acknowledgements, this desktop environment could not reliably launch a second isolated Electron app while Codex/ChatGPT Electron was active, so the current protocol's real-window smoke is intentionally deferred to the cumulative PR G harness rather than claimed as complete here.

Stacked on #4.

[hqhq1025]

The exact net diff represented here is now published upstream as apache#896. Closing this fork-local review PR to keep the active review queue in the upstream repository.