feat: Add transcription worker and state management

Introduce an `AppState` struct to hold shared application state,
including configuration and the transcription sender.
Modify `create_router` and `create_router_with_state` to use `AppState`.
Update `main.rs` to initialize the transcription worker and pass the
`AppState` to the router.
Implement the transcription worker logic in
`server/src/transcribe/worker.rs`, handling job queues, FFmpeg remuxing,
and Whisper transcription.
Update `server/src/auth.rs` to use `Arc<Config>` from the shared state.
Modify `server/src/routes/upload.rs` to enqueue transcription jobs and
handle potential errors.
Add `TranscribeJob` and channel types in `server/src/transcribe/mod.rs`.

server/src/routes/mod.rs

@@ -3,14 +3,12 @@ mod health;
 mod upload;
 mod web;
 
-use std::sync::Arc;
-
 use axum::routing::{get, post};
 use axum::Router;
 
-use crate::config::Config;
+use crate::AppState;
 
-pub fn api_router() -> Router<Arc<Config>> {
+pub fn api_router() -> Router<AppState> {
     Router::new()
         .route("/api/health", get(health::handle_health))
         .route("/api/debug/whoami", get(debug::handle_whoami))