Logging: Unify FE+BE logging with tauri-plugin-log

- Replace env_logger with tauri-plugin-log + env_filter (RUST_LOG still works)
- Add batching log bridge: FE logs → Rust log facade → terminal + file
    - 100ms batch window, consecutive dedup (×N suffix), 200/s throttle
- Shorter log format: "10:19:34.90 INFO indexing::writer  msg"
- Colored terminal output via fern
- Log file at ~/Library/Logs/ with 50 MB rotation
- Migrate feLog() call sites (viewer, updater) to getAppLogger()
- Delete ad-hoc feLog/fe_log bridge
- Wire verbose logging toggle to also set Rust log level at runtime
- "Open log file" button now opens actual log directory

Author: vdavid

AGENTS.md

@@ -61,9 +61,11 @@ Run the smallest set of checks possible for efficiency while maintaining confide
 
 ## Debugging
 
+- **Unified logging**: Frontend and backend logs appear together in the terminal and in a shared log file at
+  `~/Library/Logs/com.veszelovszki.cmdr/`. The log file is also accessible from Settings > Logging > "Open log file".
 - **Svelte/TypeScript**: Use LogTape via `getAppLogger('feature')` from `$lib/logger`. Levels: debug, info, warn, error.
   Dev mode shows info+, prod shows error+ only. Enable debug for a feature by adding to `debugCategories` in logger.ts.
-- **Rust**: Uses `env_logger` with `RUST_LOG` var. Default: info. Example: `RUST_LOG=cmdr_lib::network=debug pnpm dev`.
+- **Rust**: Uses `tauri-plugin-log` with `RUST_LOG` var. Default: info. Example: `RUST_LOG=cmdr_lib::network=debug pnpm dev`.
   It's usually worth adding `,smb=warn,sspi=warn,info` too to suppress some excessive logging from smb, unless you're
   debugging SMB issues.
 - When ran with `pnpm dev`, Cmdr hot reloads on file changes. Takes max 15s for back-end changes, max 3s on front-end.