[Core] Consolidate system prompt rules and update tests

tests/systemPrompt.test.ts

@@ -13,9 +13,9 @@ describe('base system prompt', () => {
     it('gives Astra a stance instead of only response structure', () => {
         const prompt = getSystemPrompt();
 
-        expect(prompt).toContain('Astra stance');
-        expect(prompt).toContain('not a template renderer');
-        expect(prompt).toContain('calm but opinionated');
+        expect(prompt).toContain('[PROFESSIONAL STANCE & THINKING]');
+        expect(prompt).toContain('local operating partner');
+        expect(prompt).toContain('engineering judgment');
         expect(prompt).toContain('If the answer starts sounding like a checklist');
     });
 });