feat: wire OS sleep/wake power events (suspend-edge session snapshot)

[pmaxhogan]

Closes #33.

What

Wires the OS suspend/resume power events that DESIGN s5.10 assumed but that were left as per-OS TODO seams. The orchestrator already had the on_power_event / complete_resume logic (and unit tests); nothing produced the edges in production, so the app relied on the 30s power poll (which never runs the resume sequence). Now the suspend/resume edge is detected at the edge and the s5.10.2 / s5.10.3 sequences run.

Per-platform backend choices

• Windows (verified on-host): PowerRegisterSuspendResumeNotification with DEVICE_NOTIFY_CALLBACK. The system calls our callback directly - no hidden window or message pump. Maps PBT_APMSUSPEND -> Suspending, PBT_APMRESUMEAUTOMATIC/PBT_APMRESUMESUSPEND -> Resumed.
• macOS (compile-only here): IOKit IORegisterForSystemPower on a dedicated CFRunLoop thread; kIOMessageSystemWillSleep -> Suspending, kIOMessageSystemHasPoweredOn -> Resumed, and we ack kIOMessageCanSystemSleep / will-sleep via IOAllowPowerChange so the system never blocks on us. Chosen over NSWorkspace because it is the documented C sleep/wake API, matches the existing IOKit power reader + the Windows callback shape, and needs no AppKit main-thread run loop (structurally identical to the tested Windows path).
• Linux (compile-only here): logind org.freedesktop.login1.Manager.PrepareForSleep(bool) via a zbus #[proxy]-generated signal stream (start=true -> Suspending, false -> Resumed). zbus is pinned to the tokio reactor to match the app runtime.

Plumbing

• driven-power: new SleepWakeEvent edge type, PowerSource::subscribe_sleep_wake (default inert receiver so no impl breaks), and a single uniform SleepWakeMonitor RAII handle whose per-OS teardown unregisters / stops-and-joins / aborts on drop or stop().
• driven-core: the run loop subscribes to the edge stream, maps to PowerEvent, calls on_power_event, and fires the deferred complete_resume after the 30s defer via a fixed-instant timer arm (inline, so it respects the single-in-flight guard). A suspend supersedes a stale pending resume.
• app-shell: assembly::build_account starts the monitor per account; AccountHandle holds it and tears it down on quit (no orphaned OS handle / thread / task), mirroring the existing power-poller bookkeeping.
• FakePowerSource::push_sleep_wake lets tests drive edges deterministically.

Empirically tested vs compile-only

• Empirically tested (this Windows host): the real Win32 registration + unregistration lifecycle; the exact PDEVICE_NOTIFY_CALLBACK_ROUTINE mapping suspend/resume codes to a broadcast a subscriber receives (a real machine-suspend cannot run in an automated test, so the callback is invoked directly with the OS codes); the pure PBT_* mapping; and a driven-core run-loop integration test that pushes Suspending -> Resumed through FakePowerSource and asserts the loop broadcasts the Power events and completes a from-scratch Wake cycle to Idle after the defer.
• Compile-only here (implementer builds on Windows): the macOS and Linux OS backends. Both are cross-checked and clippy-clean from Windows via cargo check/cargo clippy --target x86_64-apple-darwin and --target x86_64-unknown-linux-gnu (type-check without linking); CI's 3-OS matrix is the runtime gate. Their pure mapping fns + the subscribe/broadcast plumbing are unit-tested on every OS.

Tests added

• driven-power: Windows PBT mapping, callback->broadcast, real register/teardown lifecycle; macOS IOKit-message mapping + subscribe delivery; Linux PrepareForSleep mapping + subscribe delivery.
• driven-test-fixtures: push_sleep_wake reaches a subscriber.
• driven-core: run loop consumes sleep/wake edges and completes the deferred resume.

Notes / deferred

• Resumable upload sessions are already checkpointed per-chunk into pending_ops.payload_json (PersistedResumable{session,acked_offset}) and stale sessions are discarded by the executor's existing 6-day age check, so the "session snapshot" requirement is satisfied by that continuous persistence; this PR adds the missing edge detection + resume sequence that drives it.
• DESIGN s5.10.3 step 3 (pre-emptive token refresh on wake) is unchanged: RefreshingTokenSource refreshes on-demand on the first post-wake request. The "Suspending..." tray tooltip (s5.10.2 cosmetic) is not wired (the event bridge still ignores Power events) - deferred as a nicety.

🤖 Generated with Claude Code

https://claude.ai/code/session_014fLmkjpFkiuky72eLBijL4

[github-actions]

Coverage

Area	main	this PR	delta
Rust (lib crates)	76.76%	76.70%	-0.06 (OK)
UI (vue/ts)	88.17%	88.17%	+0.00 (OK)

Gate: passed - no coverage regression (epsilon 0.1 pp).