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/modes/rpc/rpc-mode.ts

@@ -543,7 +543,7 @@ export async function runRpcMode(session: AgentSession): Promise<never> {
 					commands.push({
 						name: template.name,
 						description: template.description,
-						source: "template",
+						source: "prompt",
 						location: template.source as RpcSlashCommand["location"],
 						path: template.filePath,
 					});

packages/coding-agent/src/modes/rpc/rpc-types.ts

@@ -77,7 +77,7 @@ export interface RpcSlashCommand {
 	/** Human-readable description */
 	description?: string;
 	/** What kind of command this is */
-	source: "extension" | "template" | "skill";
+	source: "extension" | "prompt" | "skill";
 	/** Where the command was loaded from (undefined for extensions) */
 	location?: "user" | "project" | "path";
 	/** File path to the command source */