v1.7.4: ship #275 (YouTube split) + #280 (negative-cache + pre-warm)

#275: youtube_via_relay no longer routes video/image CDNs through
Apps Script. The flag now correctly carves out only the API/HTML
hosts where Restricted Mode is enforced; video chunks come direct
from googlevideo.com (which was missing from the SNI rewrite list
entirely — fixed). Long videos no longer hit Apps Script's 6-min
execution cap, and single-chunk timeouts no longer abort playback.

#280: TunnelMux now caches "destination unreachable" responses from
the tunnel-node (Network is unreachable / No route to host) for 30
seconds, short-circuiting subsequent CONNECTs to that destination
with 502 (HTTP) or 0x04 (SOCKS5). Saves ~5 batches/second on
IPv6-only host probes. Startup pre-warm pool grew 12→24.

143/143 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -14,8 +14,8 @@ android {
         applicationId = "com.therealaleph.mhrv"
         minSdk = 24 // Android 7.0 — covers 99%+ of live devices.
         targetSdk = 34
-        versionCode = 148
-        versionName = "1.7.3"
+        versionCode = 149
+        versionName = "1.7.4"
 
         // Ship all four mainstream Android ABIs:
         //   - arm64-v8a      — 95%+ of real-world Android phones since 2019