feat(vdisplay): ship keep_alive=forever (gaming-rig) — Windows MgrState::Pinned

Completes the last §6A-era preset. The Linux registry already resolved forever→Pinned (pure
lifecycle machine); the blockers were the Windows manager, the mgmt reject, and the console tag:

- Windows manager: new `MgrState::Pinned { mon }` — the last-released monitor under keep_alive=forever
  is kept indefinitely (like Lingering but the linger timer never fires). A reconnect preempts +
  recreates it (same as Lingering — a reused IddCx swap-chain is dead), snapshot reports "pinned",
  and `force_release` (POST /display/release, the §8 escape hatch) frees a pinned monitor. release()
  branches on the new `keep_alive_forever()`; all MgrState matches made exhaustive over Pinned.
- mgmt PUT /display/settings: stop rejecting keep_alive=forever (now honored on both platforms with a
  release path). OpenAPI regenerated.
- web: un-disable the gaming-rig preset (DISABLED_PRESETS now empty) — one-click applies.

Linux paths + web/tsc/openapi green; 47 vdisplay tests pass. The Windows manager.rs is #[cfg(windows)]
(not compilable on the Linux dev box) — build-verified + on-glass validation on .173 to follow.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

api/openapi.json

@@ -268,7 +268,7 @@
           "display"
         ],
         "summary": "Set the display-management policy",
-        "description": "Persists a new policy (validated + clamped) and applies it from the next connect/teardown — a\nrunning session keeps the display it opened on. `keep_alive: forever` is rejected until the\ndisplay-lifecycle stage ships (it would keep physical monitors dark indefinitely with no release\npath yet).",
+        "description": "Persists a new policy (validated + clamped) and applies it from the next connect/teardown — a\nrunning session keeps the display it opened on. `keep_alive: forever` (the gaming-rig preset) is\nhonored (the display is Pinned; free it via `POST /display/release`).",
         "operationId": "setDisplaySettings",
         "requestBody": {
           "content": {
@@ -292,7 +292,7 @@
             }
           },
           "400": {
-            "description": "An option value is not yet supported (e.g. keep_alive forever)",
+            "description": "Malformed policy body",
             "content": {
               "application/json": {
                 "schema": {