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>

Cargo.lock

@@ -2547,6 +2547,7 @@ dependencies = [
  "jni",
  "libc",
  "log",
+ "mdns-sd",
  "ndk",
  "opus",
  "punktfunk-core",