feat: add TRANSFORM microflow action and weather demo example

Adds the Microflows$TransformJsonAction as a first-class MDL statement:

  $Result = TRANSFORM $Input WITH Module.Transformer;

Full pipeline: BSON parser, grammar rule, AST type, visitor, executor
builder, writer serializer, and DESCRIBE formatter. Version-gated to
Mendix 11.9+ (same as Data Transformers).

Also includes:
- weather-demo.mdl: end-to-end example (REST Client → TRANSFORM →
  IMPORT FROM MAPPING → page) using the Open-Meteo weather API
- Updated rest-client.md skill: documents both REST Client (new) and
  REST CALL (inline) approaches with guidance on when to use each
- Updated rest-call-from-json.md: cross-references the REST Client
  approach as the recommended path for structured APIs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako

.claude/skills/mendix/rest-call-from-json.md

@@ -1,14 +1,19 @@
 # REST Call from JSON Payload — End-to-End Skill
 
 Use this skill to generate the full stack of Mendix integration artifacts from a JSON payload:
-JSON Structure → Non-persistent entities → Import Mapping → REST CALL microflow.
+JSON Structure → Non-persistent entities → Import Mapping → microflow.
+
+> **Two approaches**: This skill uses the **inline REST CALL** approach (good for one-off calls
+> and quick prototyping). For structured APIs with reusable operations, use the **REST Client**
+> approach instead — see [rest-client.md](rest-client.md) for `CREATE REST CLIENT` + `SEND REST REQUEST`
+> + optional `TRANSFORM` with JSLT data transformers.
 
 ## Overview — Four Steps
 
 1. **CREATE JSON STRUCTURE** — store the raw payload and derive the element tree
 2. **CREATE ENTITY** (non-persistent) — one per JSON object type, with attributes per JSON field
 3. **CREATE IMPORT MAPPING** — link JSON structure elements to entities and attributes
-4. **CREATE MICROFLOW** — inline REST CALL that invokes the import mapping
+4. **CREATE MICROFLOW** — inline REST CALL that invokes the import mapping (or use REST Client + SEND REST REQUEST)
 
 ---