fix(coding-agent): rename SlashCommandSource "template" to "prompt" for consistency

BREAKING CHANGE: RPC get_commands response and SlashCommandSource type
now use "prompt" instead of "template" to match the rest of the codebase.

packages/coding-agent/src/core/agent-session.ts

@@ -1799,7 +1799,7 @@ export class AgentSession {
 			const templates: SlashCommandInfo[] = this.promptTemplates.map((template) => ({
 				name: template.name,
 				description: template.description,
-				source: "template",
+				source: "prompt",
 				location: normalizeLocation(template.source),
 				path: template.filePath,
 			}));

packages/coding-agent/src/core/slash-commands.ts

@@ -1,4 +1,4 @@
-export type SlashCommandSource = "extension" | "template" | "skill";
+export type SlashCommandSource = "extension" | "prompt" | "skill";
 
 export type SlashCommandLocation = "user" | "project" | "path";