feat(plugin): surface loaded plugin commands in command-line autocomplete

Autocomplete suggestions came only from all_registered_command_names() —
the compile-time inventory registry returning &'static str — so
runtime-loaded plugin commands could never appear. Typing a plugin's
command prefix (e.g. `LS_`) showed nothing even with the plugin loaded
and its ribbon tab active; dispatch worked, only discovery was blind.

Collect each enabled plugin's ribbon ToolDef command ids plus its
manifest command_prefixes into a dynamic candidate pool
(OwnedRibbonGroup::command_ids → PluginManager::command_names →
plugin_command_names), refreshed in rebuild_ribbon_modules on startup
load, settings reload, and every enable/disable toggle. ranked_matches
now merges this pool with the static registry and returns owned strings.

A plugin.toml `commands = [...]` list for sub-verbs with no ribbon button
(e.g. LS_AUTOLABEL) stays a follow-up — it's a plugin-API surface change.

Closes #272

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/ocs_plugin_api/src/process/manager.rs

@@ -122,6 +122,24 @@ impl PluginManager {
             .collect()
     }
 
+    /// Command names advertised by every alive, non-disabled plugin: each
+    /// ribbon tool's command id plus the manifest's `command_prefixes`. The
+    /// host merges these into command-line autocomplete so plugin commands are
+    /// discoverable by typing (#272).
+    pub fn command_names<F: Fn(&str) -> bool>(&self, is_disabled: F) -> Vec<String> {
+        let mut out = Vec::new();
+        for p in &self.plugins {
+            if is_disabled(p.process.id()) || !p.process.is_alive() {
+                continue;
+            }
+            for group in p.process.ribbon() {
+                out.append(&mut group.command_ids());
+            }
+            out.extend(p.process.manifest().command_prefixes.iter().cloned());
+        }
+        out
+    }
+
     /// Begin asynchronous shutdown of every plugin process.
     ///
     /// Kills every child synchronously on the calling thread and moves the