fix(desktop): preserve responsiveness across idle and media pressure

[rldyourmnd]

Idle native sessions could wait for a full video reconnect even while the control channel still responded. The macOS activity allowed idle system sleep, and full-queue motion eviction could remove the position belonging to an earlier click. Sustained delayed media receipts also escaped the existing bitrate-pressure observation.

The viewer now requests recovery images at three and eight seconds without decoded progress before the existing fifteen-second reconnect. Its scoped macOS activity prevents automatic idle system sleep while preserving display sleep and screen locking. Only adjacent absolute pointer motion on the same display coalesces; the bounded 1024-entry queue preserves position barriers and fails closed at overflow. Input-ACK tracking has the same burst capacity and exposes matched, unmatched and evicted observations. The serving controller observes sustained completed delayed receipts with the existing reduction and recovery bounds.

Validation on macOS arm64:

• Standard workspace tests: 795 passed, no failures, two native X11 tests ignored.
• Desktop-feature workspace tests: 827 passed, no failures, two native X11 tests ignored.
• Default and desktop-feature workspace/all-target strict clippy, fmt and cargo-deny passed.
• Focused controls/render suites cover repair on the original framed channel, the unrecovered deadline, cancellation, 800 button edges and delayed ACKs, position barriers at full capacity and macOS activity option bits. These render tests require the viewer feature.
• The first broad run hit the test shell's 256-descriptor limit. Local-manager and complete workspace reruns used a process-local limit of 4096; the initial failure is retained in the qualification report.

Remote wire formats, identity, authorization and unrelated managed streams remain unchanged. The qualification report separates regression evidence from installed visibility, long idle, sleep/network-change and physical input-to-pixel acceptance. Fresh Linux/macOS CI belongs to this exact PR head; earlier green runs are not reused as its results.