Add get_commands RPC for headless clients (#995)

* Add get_commands RPC for headless clients

Headless clients like Emacs can now query which commands are available.
Previously they could only discover file-based prompt templates by
scanning the filesystem; extension commands and skills were invisible.

The response includes each command's name, description, and source
(extension, template, or skill). Commands appear in the same order
as the TUI's autocomplete: extension commands first, then templates,
then skills.

Built-in TUI commands (/settings, /fork, etc.) are excluded since
they require the interactive UI. Commands like /compact have dedicated
RPC equivalents instead.

* Add location and path to get_commands response

Clients can show where commands come from (user/project/path) and
display file paths in tooltips. The data is already available on
templates and skills - just exposing it.

packages/coding-agent/src/core/extensions/runner.ts

@@ -372,6 +372,16 @@ export class ExtensionRunner {
 		return commands;
 	}
 
+	getRegisteredCommandsWithPaths(): Array<{ command: RegisteredCommand; extensionPath: string }> {
+		const result: Array<{ command: RegisteredCommand; extensionPath: string }> = [];
+		for (const ext of this.extensions) {
+			for (const command of ext.commands.values()) {
+				result.push({ command, extensionPath: ext.path });
+			}
+		}
+		return result;
+	}
+
 	getCommand(name: string): RegisteredCommand | undefined {
 		for (const ext of this.extensions) {
 			const command = ext.commands.get(name);

packages/coding-agent/src/core/prompt-templates.ts

@@ -11,7 +11,7 @@ export interface PromptTemplate {
 	name: string;
 	description: string;
 	content: string;
-	source: string; // e.g., "user", "project", "path", "inline"
+	source: string; // "user", "project", or "path"
 	filePath: string; // Absolute path to the template file
 }