Add VideoWall feature: server-side preview clip generation and mobile grid view

Backend (Rust/Actix-web):
- Add video_preview_clips table and PreviewDao for tracking preview generation
- Add ffmpeg preview clip generator: 10 equally-spaced 1s segments at 480p with CUDA NVENC auto-detection
- Add PreviewClipGenerator actor with semaphore-limited concurrent processing
- Add GET /video/preview and POST /video/preview/status endpoints
- Extend file watcher to detect and queue previews for new videos
- Use relative paths consistently for DB storage (matching EXIF convention)

Frontend (React Native/Expo):
- Add VideoWall grid view with 2-3 column layout of looping preview clips
- Add VideoWallItem component with ActiveVideoPlayer sub-component for lifecycle management
- Add useVideoWall hook for batch status polling with 5s refresh
- Add navigation button in grid header (visible when videos exist)
- Use TextureView surface type to fix Android z-ordering issues
- Optimize memory: players only mount while visible via FlatList windowSize
- Configure ExoPlayer buffer options and caching for short clips
- Tap to toggle audio focus, long press to open in full viewer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/state.rs

@@ -4,7 +4,10 @@ use crate::database::{
     SqliteCalendarEventDao, SqliteDailySummaryDao, SqliteExifDao, SqliteInsightDao,
     SqliteLocationHistoryDao, SqliteSearchHistoryDao,
 };
-use crate::video::actors::{PlaylistGenerator, StreamActor, VideoPlaylistManager};
+use crate::database::{PreviewDao, SqlitePreviewDao};
+use crate::video::actors::{
+    PlaylistGenerator, PreviewClipGenerator, StreamActor, VideoPlaylistManager,
+};
 use actix::{Actor, Addr};
 use std::env;
 use std::sync::{Arc, Mutex};
@@ -12,10 +15,12 @@ use std::sync::{Arc, Mutex};
 pub struct AppState {
     pub stream_manager: Arc<Addr<StreamActor>>,
     pub playlist_manager: Arc<Addr<VideoPlaylistManager>>,
+    pub preview_clip_generator: Arc<Addr<PreviewClipGenerator>>,
     pub base_path: String,
     pub thumbnail_path: String,
     pub video_path: String,
     pub gif_path: String,
+    pub preview_clips_path: String,
     pub excluded_dirs: Vec<String>,
     pub ollama: OllamaClient,
     pub sms_client: SmsApiClient,
@@ -29,22 +34,32 @@ impl AppState {
         thumbnail_path: String,
         video_path: String,
         gif_path: String,
+        preview_clips_path: String,
         excluded_dirs: Vec<String>,
         ollama: OllamaClient,
         sms_client: SmsApiClient,
         insight_generator: InsightGenerator,
+        preview_dao: Arc<Mutex<Box<dyn PreviewDao>>>,
     ) -> Self {
         let playlist_generator = PlaylistGenerator::new();
         let video_playlist_manager =
             VideoPlaylistManager::new(video_path.clone(), playlist_generator.start());
 
+        let preview_clip_generator = PreviewClipGenerator::new(
+            preview_clips_path.clone(),
+            base_path.clone(),
+            preview_dao,
+        );
+
         Self {
             stream_manager,
             playlist_manager: Arc::new(video_playlist_manager.start()),
+            preview_clip_generator: Arc::new(preview_clip_generator.start()),
             base_path,
             thumbnail_path,
             video_path,
             gif_path,
+            preview_clips_path,
             excluded_dirs,
             ollama,
             sms_client,
@@ -94,6 +109,8 @@ impl Default for AppState {
             Arc::new(Mutex::new(Box::new(SqliteExifDao::new())));
         let daily_summary_dao: Arc<Mutex<Box<dyn DailySummaryDao>>> =
             Arc::new(Mutex::new(Box::new(SqliteDailySummaryDao::new())));
+        let preview_dao: Arc<Mutex<Box<dyn PreviewDao>>> =
+            Arc::new(Mutex::new(Box::new(SqlitePreviewDao::new())));
 
         // Initialize Google Takeout DAOs
         let calendar_dao: Arc<Mutex<Box<dyn CalendarEventDao>>> =
@@ -119,16 +136,23 @@ impl Default for AppState {
             base_path.clone(),
         );
 
+        // Ensure preview clips directory exists
+        let preview_clips_path = env::var("PREVIEW_CLIPS_DIRECTORY")
+            .unwrap_or_else(|_| "preview_clips".to_string());
+        std::fs::create_dir_all(&preview_clips_path).expect("Failed to create PREVIEW_CLIPS_DIRECTORY");
+
         Self::new(
             Arc::new(StreamActor {}.start()),
             base_path,
             env::var("THUMBNAILS").expect("THUMBNAILS was not set in the env"),
             env::var("VIDEO_PATH").expect("VIDEO_PATH was not set in the env"),
             env::var("GIFS_DIRECTORY").expect("GIFS_DIRECTORY was not set in the env"),
+            preview_clips_path,
             Self::parse_excluded_dirs(),
             ollama,
             sms_client,
             insight_generator,
+            preview_dao,
         )
     }
 }
@@ -142,10 +166,11 @@ impl AppState {
         let temp_dir = tempfile::tempdir().expect("Failed to create temp directory");
         let base_path = temp_dir.path().to_path_buf();
 
-        // Create subdirectories for thumbnails, videos, and gifs
+        // Create subdirectories for thumbnails, videos, gifs, and preview clips
         let thumbnail_path = create_test_subdir(&base_path, "thumbnails");
         let video_path = create_test_subdir(&base_path, "videos");
         let gif_path = create_test_subdir(&base_path, "gifs");
+        let preview_clips_path = create_test_subdir(&base_path, "preview_clips");
 
         // Initialize test AI clients
         let ollama = OllamaClient::new(
@@ -186,6 +211,10 @@ impl AppState {
             base_path_str.clone(),
         );
 
+        // Initialize test preview DAO
+        let preview_dao: Arc<Mutex<Box<dyn PreviewDao>>> =
+            Arc::new(Mutex::new(Box::new(SqlitePreviewDao::new())));
+
         // Create the AppState with the temporary paths
         AppState::new(
             Arc::new(StreamActor {}.start()),
@@ -193,10 +222,12 @@ impl AppState {
             thumbnail_path.to_string_lossy().to_string(),
             video_path.to_string_lossy().to_string(),
             gif_path.to_string_lossy().to_string(),
+            preview_clips_path.to_string_lossy().to_string(),
             Vec::new(), // No excluded directories for test state
             ollama,
             sms_client,
             insight_generator,
+            preview_dao,
         )
     }
 }