Add Text_Input $max_length requirement and Model.field_length() API

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

docs/CLAUDE.dist.md

@@ -698,6 +698,7 @@ Pattern recognition:
 - `Form_Utils.apply_form_errors()` for validation
 - Action loads data, Controller saves it
 - `$disabled=true` still returns values (unlike HTML)
+- **Text_Input requires `$max_length`**: Use `Model.field_length('column')` for database-driven limits, numeric value for custom, or `-1` for unlimited
 
 **Detailed guidance in `forms` skill** - auto-activates when building forms.