feat(commandline): autocomplete suggestions + inventory-based registry

Type-as-you-go suggestion popup above the input that filters known
command names by substring (so `LEADER` surfaces both LEADER and
MLEADER). Up / Down navigates the list, Enter dispatches the
highlighted entry, clicking a row dispatches directly. Esc on a
non-empty input clears the buffer instead of escalating to
command-cancel.

The name corpus comes from `inventory::submit!` blocks placed next
to each `CadCommand` impl rather than a hand-maintained static list.
Adding a new interactive command means dropping one `inventory::submit!`
line in its own module file — the autocomplete picks it up at the
next compile. 98 submissions seeded across 60 module files;
`command::all_registered_command_names()` flattens them at runtime.

One-shot dispatch arms in `app/commands.rs` (NEW, OPEN, SAVE, UNDO,
…) don't have a `CadCommand` impl and are therefore absent from
autocomplete by design.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Cargo.toml

@@ -19,6 +19,7 @@ flate2 = "1"
 image = { version = "0.25", default-features = false, features = ["png", "jpeg", "bmp", "tiff"] }
 rayon = "1"
 ureq = { version = "3", default-features = false, features = ["rustls"] }
+inventory = "0.3"
 
 [target.'cfg(target_os = "windows")'.dependencies]
 windows-sys = { version = "0.61", features = ["Win32_UI_Shell", "Win32_UI_WindowsAndMessaging"] }