feat: enhanced subagent config, reviewer output schema, and consolidated discovery helpers

- Added thinkingLevel field to agent frontmatter allowing subagents to override thinking level with clamping to model capabilities.
- Added structured output schema to reviewer agent ensuring consistent review output format with findings, correctness verdict, and confidence.
- Expanded system prompt with defensive reasoning guidance including assumption checks, edge case awareness, and completion reflex inhibition.
- Consolidated expandPath, parseFrontmatter, and parseAgentFields utilities into discovery/helpers module eliminating code duplication across loaders.
- Replaced silent error handling with logger.warn calls across config parsing, migrations, extension loading, and OAuth refresh failures.

packages/coding-agent/src/cli/update-cli.ts

@@ -144,8 +144,8 @@ async function updateViaBun(): Promise<void> {
 	try {
 		execSync(`bun update -g ${PACKAGE}`, { stdio: "inherit" });
 		console.log(chalk.green(`\n${theme.status.success} Update complete`));
-	} catch {
-		throw new Error("bun update failed");
+	} catch (error) {
+		throw new Error("bun update failed", { cause: error });
 	}
 }