Add changeset for breaking change: strict validation by default

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

.changeset/strict-validation-by-default.md

@@ -0,0 +1,63 @@
+---
+"@objectstack/spec": major
+---
+
+**Breaking Change: Strict Validation Enabled by Default**
+
+`defineStack()` now validates configurations by default to enforce naming conventions and catch errors early.
+
+**What Changed:**
+- `defineStack()` now defaults to `strict: true` (was `strict: false`)
+- Field names are now validated to ensure snake_case format
+- Object names, field types, and all schema definitions are validated
+
+**Migration Guide:**
+
+If you have existing code that violates naming conventions:
+
+```typescript
+// Before (would silently accept invalid names):
+defineStack({
+  manifest: {...},
+  objects: [{
+    name: 'my_object',
+    fields: {
+      firstName: { type: 'text' }  // ❌ Invalid: camelCase
+    }
+  }]
+});
+
+// After (will throw validation error):
+// Error: Field names must be lowercase snake_case
+
+// Fix: Use snake_case
+defineStack({
+  manifest: {...},
+  objects: [{
+    name: 'my_object',
+    fields: {
+      first_name: { type: 'text' }  // ✅ Valid: snake_case
+    }
+  }]
+});
+```
+
+**Temporary Workaround:**
+
+If you need to temporarily disable validation while fixing your code:
+
+```typescript
+defineStack(config, { strict: false });  // Bypass validation
+```
+
+**Why This Change:**
+
+1. **Catches Errors Early**: Invalid field names caught during development, not runtime
+2. **Enforces Conventions**: Ensures consistent snake_case naming across all projects
+3. **Prevents AI Hallucinations**: AI-generated objects must follow proper conventions
+4. **Database Compatibility**: snake_case prevents case-sensitivity issues in queries
+
+**Impact:**
+
+- Projects with properly named fields (snake_case): ✅ No changes needed
+- Projects with camelCase/PascalCase fields: ⚠️ Must update field names or use `strict: false`