feat(android): native mDNS discovery, host naming, touch mouse, stock selects

Discovery: replace the flaky per-OEM NsdManager with the same mdns-sd browse
the Linux/Windows clients use, in the Rust core over JNI and polled by Kotlin
(discovery.rs + nativeDiscovery{Start,Poll,Stop}); Kotlin keeps only the Wi-Fi
MulticastLock + permission UX. IPv4-only (the core can't dial a bare/scoped v6
literal); daemon + fold-thread cleanup on every failure path; field
sanitization so a rogue advert can't corrupt the picker snapshot. Discovery
now starts regardless of NEARBY_WIFI_DEVICES (raw multicast only needs the
MulticastLock) — a denial no longer kills it forever. ParseTxtTest replaced by
ParseRecordTest.

Hosts: hide already-saved hosts from the "Discovered" section (match by
fingerprint, else address:port — mirrors the Apple client); add an optional
Name field to the Add-host sheet and a Rename action on saved cards.

Input: touch -> absolute mouse "direct pointing" like the Apple client — the
host cursor follows the finger (new nativeSendPointerAbs -> MouseMoveAbs). Tap
= left click, two-finger tap = right click, two-finger drag = scroll,
tap-then-drag = left-drag, three-finger tap = HUD toggle.

Settings: revert the dropdowns to the stock ExposedDropdownMenuBox look (a
controller-focus UI will come separately); even out the Add-host field gaps.

Docs updated (CLAUDE.md, client READMEs, docs-site status).

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

clients/android/app/src/main/AndroidManifest.xml

@@ -4,11 +4,13 @@
     <!-- punktfunk/1 QUIC/UDP data plane. -->
     <uses-permission android:name="android.permission.INTERNET" />
     <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
-    <!-- mDNS discovery of _punktfunk._udp on the LAN (NsdManager). -->
+    <!-- mDNS discovery of _punktfunk._udp on the LAN (native mdns-sd browse). Requested
+         opportunistically — raw multicast reception needs only the MulticastLock, not this. -->
     <uses-permission
         android:name="android.permission.NEARBY_WIFI_DEVICES"
         android:usesPermissionFlags="neverForLocation" />
-    <!-- Hold a MulticastLock while NsdManager discovery runs (OEM Wi-Fi power-save hedge). -->
+    <!-- HostDiscovery holds a MulticastLock while the native mDNS browse runs — raw multicast
+         reception needs it (also an OEM Wi-Fi power-save hedge). -->
     <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />
     <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
     <!-- Enforced from Android 17 (SDK 37) for ALL local-network traffic incl. the QUIC socket.