feat: implement video_protocol.rs, commands.rs, wire up main.rs, and index.html

- video_protocol.rs: tutdock:// custom protocol with HTTP Range support
  for video streaming, subtitle/font serving with path traversal protection
- commands.rs: all 26 Tauri command handlers as thin wrappers
- main.rs: full Tauri bootstrap with state management, window restore,
  async font caching, and ffmpeg discovery
- index.html: complete HTML markup extracted from Python app
- lib.rs: updated with all module declarations and AppPaths struct

src-tauri/src/lib.rs

@@ -1,3 +1,6 @@
+use std::path::PathBuf;
+
+pub mod commands;
 pub mod ffmpeg;
 pub mod fonts;
 pub mod library;
@@ -6,11 +9,13 @@ pub mod recents;
 pub mod state;
 pub mod subtitles;
 pub mod utils;
+pub mod video_protocol;
 
-#[cfg_attr(mobile, tauri::mobile_entry_point)]
-pub fn run() {
-    tauri::Builder::default()
-        .plugin(tauri_plugin_dialog::init())
-        .run(tauri::generate_context!())
-        .expect("error while running tauri application");
+/// Application directory paths resolved at startup, managed as Tauri state.
+pub struct AppPaths {
+    pub exe_dir: PathBuf,
+    pub state_dir: PathBuf,
+    pub fonts_dir: PathBuf,
+    pub fa_dir: PathBuf,
+    pub subs_dir: PathBuf,
 }