feat(host,web): experimental PnP monitor-devnode disable for Exclusive sessions

Second experiment against the connected-but-dark-head stutter (field-proven
on the reporter's box: unplugging his standby HDMI TV removes a metronomic
~4 s double-jolt; DDC/CI is a dead end for TVs — measured on the lab LG, VCP
0xD6 gets no I2C ACK). An Exclusive isolate only removes physical monitors
from the CCD topology; their PnP devnodes stay live, so every standby wake
(auto input scan, Instant-On HPD cycling) still triggers the full Windows
reaction: PnP arrival/removal, CCD re-evaluation, DWM invalidation — the
suspected hiccup mechanism (Apollo #368's Device-Manager-refresh signature).

- New `pnp_disable_monitors` display-policy axis (default off): orthogonal
  to presets like game_session/ddc_power_off, surfaced in GET/PUT
  /display/settings + the enforced list, carried through the layout
  transform.
- windows/monitor_devnode.rs: after the isolate takes, disable exactly the
  deactivated monitors' devnodes — CCD target → monitor device path
  (DISPLAYCONFIG_TARGET_DEVICE_NAME) → PnP instance id → CM_Disable_DevNode
  with CM_DISABLE_PERSIST, so a hot-plug RE-ARRIVAL stays disabled (that
  persistence is the whole point). Teardown re-enables BEFORE the CCD
  restore (+300 ms re-arrival settle) so restored paths have their monitors
  back. Precise selection — co-installed third-party virtual displays are
  never touched.
- Crash safety: instance ids journal to <config>/pnp-disabled-monitors.json
  before disabling; serve startup re-enables leftovers from a crashed host.
  Worst case is documented in the console help (Device Manager re-enable).
- Web console: second Experimental-badged toggle (the DDC block refactored
  into a shared ExperimentalToggle), EN/DE strings, preset-switch carry.

Verified: Linux 263 tests + clippy + fmt clean; Windows (RTX box) 220/220 +
clippy clean; web tsc + production build clean; openapi.json regenerated.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

api/openapi.json

@@ -2543,6 +2543,10 @@
           "mode_conflict": {
             "$ref": "#/components/schemas/ModeConflict"
           },
+          "pnp_disable_monitors": {
+            "type": "boolean",
+            "description": "EXPERIMENTAL (Windows): after an `Exclusive` isolate deactivates the physical monitors,\nadditionally DISABLE their PnP device nodes (persistently, so a standby monitor/TV whose\nhot-plug events re-arrive stays disabled) and re-enable them at restore. Targets the same\n\"connected-but-dark head\" periodic-stutter class as [`Self::ddc_power_off`], but at the\nWindows-reaction level: a disabled devnode's wake events trigger no PnP arrival, no CCD\nre-evaluation, no DWM invalidation. A crash-recovery journal re-enables leftovers on host\nstartup. Orthogonal to `preset` (like `game_session`); `#[serde(default)]` = off."
+          },
           "preset": {
             "$ref": "#/components/schemas/Preset"
           },