fix(security): land the 2026-07 audit fixes — SSRF guards, roster lane, SYSTEM path hygiene

The low/medium findings from the July host+Windows security review, as
implemented in the audit session's working tree:

- Webhooks and library-art fetches refuse loopback/link-local/metadata
  targets and no longer follow redirects (SSRF pivots from the privileged
  host process).
- The paired-client rosters (/clients, /native/clients) move off the
  streaming-client auth lane — one paired device could enumerate every other
  device's name + fingerprint; only the bearer/loopback console keeps them.
- Device-name sanitizing extends to bidi/format control characters
  (spoofable rendering) via the shared native_pairing::is_spoofy_char;
  stream-marker quoting uses the same set.
- The SYSTEM service resolves powershell by its full System32 path —
  CreateProcess checks the launching EXE's own directory first, so a planted
  powershell.exe beside the host binary would have run as SYSTEM.
- The pf-vdisplay driver's opt-in file log moves from world-writable
  C:\Users\Public to WUDFHost's own temp dir.
- GameStream pairing sessions are single-use (removed whatever the outcome).
- Uninstall also removes the pf_mouse driver-store entry (rider from the
  virtual-HID-mouse work).
- openapi.json regenerated (hardened-config-dir doc wording).

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

api/openapi.json

@@ -2744,7 +2744,7 @@
       },
       "CustomEntry": {
         "type": "object",
-        "description": "A user-added title, persisted in `~/.config/punktfunk/library.json`. Same shape the API\nreturns and the web console edits.",
+        "description": "A user-added title, persisted in the hardened host config dir's `library.json` (see\n[`custom_path`]). Same shape the API returns and the web console edits.",
         "required": [
           "id",
           "title"