Add Android app with full TUN bridge + two proxy fixes the desktop also wants (#29)

The app is a Kotlin/Compose front-end that reuses the mhrv-rs crate
via JNI. It speaks VpnService to get a TUN fd, hands that to tun2proxy,
and funnels every app's traffic through the in-process SOCKS5 listener —
no per-app proxy setup on the device.

Two fixes in `src/proxy_server.rs` apply to desktop builds too:

* SNI peek via `LazyConfigAcceptor`. When a browser uses DoH (Chrome's
  default), tun2proxy hands us a raw IP in the SOCKS5 CONNECT. Minting
  a MITM cert for the IP produced `ERR_CERT_COMMON_NAME_INVALID` on
  Cloudflare-fronted sites. We now read the ClientHello's SNI first
  and use that both as the cert subject and as the upstream host for
  the Apps Script relay (fetching `https://<IP>/...` with an IP in the
  Host header gets rejected by CF anyway).
* Short-circuit CORS preflight at the MITM boundary. `UrlFetchApp.fetch()`
  rejects `OPTIONS` with a Swedish "Ett attribut med ogiltigt värde
  har angetts: method" error, which silently broke every fetch()/XHR
  preflight and was the root cause of "JS doesn't load" on Discord,
  Yahoo, and similar. Since we already terminate the TLS the browser
  talks to, answering the preflight with a permissive 204 is safe —
  the real request still goes through the relay.

Android-side capabilities (feature-parity with `mhrv-rs-ui` where it
fits on a phone):

* multi-deployment ID editor
* SNI rotation pool + per-SNI "Test" + "Test all" (JNI into scan_sni)
* live logs panel (JNI ring buffer drained on a 500 ms poll)
* Advanced section: verify_ssl, parallel_relay, log_level, upstream_socks5
* CA install flow that matches modern Android's reality: saves
  `Downloads/mhrv-ca.crt` via MediaStore, deep-links Security settings,
  then verifies post-hoc by fingerprint lookup in AndroidCAStore (the
  KeyChain intent dead-ends with a Close-only dialog on Android 11+)
* Start/Stop debounced to dodge an emulator EGL renderer crash on
  rapid taps

Theme matches the desktop palette exactly — always-dark, accent
`#4678B4`, card fill `#1C1E22`, 4dp button / 6dp card radii.
No dynamic color, no light scheme: the desktop is always dark and
we follow.

Build wiring:

* `Cargo.toml`: `cdylib` crate-type added; `jni` + `tun2proxy`
  scoped to `cfg(target_os = "android")` so desktop builds pay
  nothing.
* `src/data_dir.rs`: `set_data_dir()` override so the Android app's
  private filesDir replaces the `directories` crate's desktop default.
* `src/android_jni.rs`: JNI entry points for start/stop/exportCa plus
  a ring buffer draining to `Native.drainLogs()` and `testSni()` that
  wraps `scan_sni::probe_one`.
* Gradle task chain runs `cargo ndk` before each assemble; post-step
  normalizes tun2proxy's hash-suffixed cdylib to a stable filename
  so `System.loadLibrary("tun2proxy")` works.

Verified end-to-end on an API 34 emulator: ipleak, yahoo, discord,
cloudflare.com all render; TLS is MITM-ed under our user-installed
CA; service survives rapid Stop/Start cycles.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

android/gradlew.bat

@@ -0,0 +1,93 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -jar "%APP_HOME%\gradle\wrapper\gradle-wrapper.jar" %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega