refactor: replace vim keybindings with mouse navigation, remove mock data

- Remove all sample/mock data (artists, albums, tracks, queue, history, calendar)
- Delete input module (vim.rs, leader.rs) and related UI (which_key, cmdline)
- Add mouse support: click tabs, click list items, scroll wheel navigation
- Show real disk space via nix::statvfs instead of hardcoded value
- Simplify topbar/statusbar by removing mode display and key hints
- Hide album/track sections when no artist is selected

Cargo.lock

@@ -65,6 +65,12 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
 
+[[package]]
+name = "cfg_aliases"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "613afe47fcd5fac7ccf1db93babcb082c5994d996f20b8b159f2ad1658eb5724"
+
 [[package]]
 name = "color-eyre"
 version = "0.6.5"
@@ -344,6 +350,18 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "nix"
+version = "0.29.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "71e2746dc3a24dd78b3cfcb7be93368c6de9963d30f43a6a73998a9cf4b17b46"
+dependencies = [
+ "bitflags",
+ "cfg-if",
+ "cfg_aliases",
+ "libc",
+]
+
 [[package]]
 name = "object"
 version = "0.37.3"
@@ -632,6 +650,7 @@ version = "0.1.0"
 dependencies = [
  "color-eyre",
  "crossterm",
+ "nix",
  "ratatui",
 ]