refactor: apply Rust best practices across all source files

[Copilot]

Systematic Rust idiom cleanup across the entire codebase — eliminating panic-prone patterns, reducing code duplication, and improving idiomatic style.

Bug fixes (potential panics)

• psd_to_png: Logged error then unwrap()-ed anyway — would still panic. Replaced with ? propagation and proper ok_or_else on RgbaImage::from_raw
• selected_file.rs: .ok().unwrap() on COM query() call — silently converted to panic. Changed to let _ = ...
• tray.rs: store(...).unwrap() in event handler — replaced with let-else + log
• utils/mod.rs: metadata().unwrap() — replaced with .ok()?
• selected_file.rs: GetItemAt(i).unwrap() in loop — replaced with let Ok(...) else { continue }

Duplicate plugin registration

tauri_plugin_store was registered twice in lib.rs; removed the duplicate.

is_err()/is_none() + unwrap() antipattern → let-else / match

All occurrences across selected_file.rs, preview.rs, tray.rs, and command.rs replaced with idiomatic patterns.

Repetition elimination

config.rs had 16 identical chains of .get(key).unwrap().as_array().unwrap().iter().map(|v| v.as_str().unwrap().to_string()).collect(). Extracted into a single extract_str_vec helper; file shrunk from ~170 to ~65 lines.

Minor idioms

File	Before	After
audio.rs	title: title, .get(0)	field shorthand, .first()
monitor.rs	manual impl Default	#[derive(Default)]
utils/mod.rs	is_file() == false, match { Some => Some, None => None }	!is_file(), .map()
tar.rs (×4)	format!("{}", x.to_rfc3339())	x.to_rfc3339()
ffmp.rs	"seg_%03d.ts".to_string() stored in variable	inline &str literals
docs/lib.rs	index loop for i in 0..len { push(record[i]) }	.iter().map().collect()