fix(config): change no_tools_mode default to false for pi_embedded

The previous default of true was overly restrictive. false is the correct
default — tool-like prompts fall through to native handling only when
explicitly enabled.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/config/schema.test.ts

@@ -507,7 +507,7 @@ describe('configSchema — backends', () => {
     expect(result.backends.codex.enabled).toBe(false);
     expect(result.backends.gemini.enabled).toBe(false);
     expect(result.backends.pi_embedded.enabled).toBe(false);
-    expect(result.backends.pi_embedded.no_tools_mode).toBe(true);
+    expect(result.backends.pi_embedded.no_tools_mode).toBe(false);
     expect(result.backends.pi_embedded.system_prompt_mode).toBe('hybrid');
     expect(result.backends.native.enabled).toBe(true);
   });

src/config/schema.ts

@@ -212,7 +212,7 @@ const backendsSchema = z.object({
   pi_embedded: z.object({
     enabled: z.boolean().default(false),
     timeout_ms: z.number().min(1_000).max(600_000).default(120_000),
-    no_tools_mode: z.boolean().default(true),
+    no_tools_mode: z.boolean().default(false),
     model: z.string().optional(),
     system_prompt_mode: z.enum(['flynn', 'pi_default', 'hybrid']).default('hybrid'),
     module: z.string().optional(),