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/app/view.rs

@@ -508,7 +508,10 @@ impl OpenCADStudio {
         // viewport stack rather than as a separate row in the main
         // column — frees up vertical space when no command is active
         // and keeps the input close to where the cursor is drawing.
-        let command_line_overlay = iced::widget::container(self.command_line.view())
+        // Autocomplete shows only when no command is collecting its
+        // own input (otherwise typed prefixes are coordinates / values).
+        let allow_autocomplete = tab.active_cmd.is_none();
+        let command_line_overlay = iced::widget::container(self.command_line.view(allow_autocomplete))
             .width(Fill)
             .height(Fill)
             .align_x(iced::alignment::Horizontal::Center)