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>

src/modules/annotate/dim_continue.rs

@@ -158,3 +158,7 @@ impl CadCommand for DimContinueCommand {
 fn v3(p: Vec3) -> Vector3 {
     Vector3::new(p.x as f64, p.y as f64, p.z as f64)
 }
+
+
+// ── Autocomplete registry ─────────────────────────────────
+inventory::submit!(crate::command::CommandRegistration { names: &["DCO", "DIMCONTINUE"] });  // DimContinueCommand