feat: media_async + media_index modules, media_files table, tests

- media_async: thread-per-task async engine with primitives (sha256, sign, copy, uuid, file_size)
- media_index: media_files DB table with register_async for indexing chunks
- chat_msg: async media submission via register_async, simplified chat_msg_submit fields
- voice_recorder/attachment_sender: write single file (no chunk splitting on caller side)
- inputbar/messagelist: updated to new simplified submit interface
- test_media_async: 4-thread stress test (200K ops / 2 sec, 0 errors)
- test_media_index: 9 cases covering commit edge cases + async flow
- build: Makefile.am, CMakeLists.txt, utun_sources.cmake updated

lib/audio_compressor.h

@@ -17,7 +17,7 @@ typedef struct {
     int lookback_ms;
     int lookahead_ms;
     float max_gain_db;
-    float rise_rate_per_500ms;
+    float rise_rate_per_sec;
     float target_level;
 } audio_compressor_config_t;