feat: SHOW/DESCRIBE/CREATE/DROP JSON STRUCTURE (#80)

* feat: add JSON STRUCTURE DDL commands and catalog integration. Adds CREATE/DROP/SHOW/DESCRIBE JSON STRUCTURE statements for defining
JSON structures

- Add JSON STRUCTURE grammar rules with SNIPPET and CUSTOM NAME MAP
- Add json_structures catalog table tracking element count and snippet
- Add STRUCTURES and CUSTOM_NAME_MAP lexer tokens
- Add ShowJsonStructures and DescribeJsonStructure to AST query types
- Add buildJsonStructures() to catalog builder

* bug fix UTF-8 refactor: simplify capitalizeFirstRune using unicode.ToUpper. Replace strings.ToUpper roundtrip with direct unicode.ToUpper call for cleaner single-rune capitalization.

* fix: address review feedback on JSON STRUCTURE PR

- Sort custom name map keys for deterministic DESCRIBE output
- Check errors from json.Decoder.Token() and Decode() in snippet parser
- Add comment explaining why JsonElement uses int32 (verified vs Studio Pro)

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

---------

Co-authored-by: Andrej Koelewijn <andrej@koelewijn.net>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people

.claude/skills/mendix/rest-client.md

@@ -8,6 +8,34 @@ Use this skill when creating, modifying, or calling Consumed REST Clients in MDL
 - Calling REST service operations from microflows (`SEND REST REQUEST`)
 - Listing or inspecting REST clients (`SHOW REST CLIENTS`, `DESCRIBE REST CLIENT`)
 
+## JSON Structures
+
+Define JSON structures from a sample snippet before creating import/export mappings.
+
+```sql
+CREATE JSON STRUCTURE Module.Name SNIPPET '{"id": 1, "name": "John"}';
+
+-- Multi-line (use $$ quoting)
+CREATE JSON STRUCTURE Module.Name SNIPPET $${ "id": 1, "items": [{"name": "A"}] }$$;
+
+-- With documentation
+CREATE JSON STRUCTURE Module.Name COMMENT 'API response' SNIPPET '...';
+
+-- Custom name mapping for non-English keys
+CREATE JSON STRUCTURE Module.Name SNIPPET $${"kvkNummer": "123"}$$
+CUSTOM NAME MAP ('kvkNummer' AS 'ChamberOfCommerceNumber');
+
+-- Idempotent update
+CREATE OR REPLACE JSON STRUCTURE Module.Name SNIPPET '...';
+
+-- Browse and delete
+SHOW JSON STRUCTURES;
+DESCRIBE JSON STRUCTURE Module.Name;
+DROP JSON STRUCTURE Module.Name;
+```
+
+Type inference: ISO 8601 strings → DateTime, integers → Integer, decimals → Decimal, booleans → Boolean. Snippet is auto-formatted when stored.
+
 ## CREATE REST CLIENT
 
 ```sql

cmd/mxcli/lsp_completions_gen.go

@@ -332,6 +332,18 @@ CREATE OR REPLACE NAVIGATION Responsive
 
 **Export levels:** `'Hidden'` (default, internal to module), `'Public'` (accessible from other modules).
 
+## JSON Structures
+
+| Statement | Syntax | Notes |
+|-----------|--------|-------|
+| Show structures | `SHOW JSON STRUCTURES [IN Module];` | List all or filter by module |
+| Describe structure | `DESCRIBE JSON STRUCTURE Module.Name;` | Re-executable CREATE OR REPLACE + element tree |
+| Create structure | `CREATE JSON STRUCTURE Module.Name [COMMENT 'text'] SNIPPET '...json...';` | Element tree auto-built from snippet |
+| Create (multi-line) | `CREATE JSON STRUCTURE Module.Name SNIPPET $${ "key": "value" }$$;` | Dollar-quoted snippet for readability |
+| Create or replace | `CREATE OR REPLACE JSON STRUCTURE Module.Name SNIPPET '...';` | Idempotent — preferred for AI agents |
+| Create with name map | `CREATE JSON STRUCTURE Module.Name SNIPPET '...' CUSTOM NAME MAP ('jsonKey' AS 'CustomName', ...);` | Override auto-generated ExposedNames |
+| Drop structure | `DROP JSON STRUCTURE Module.Name;` | |
+
 ## Java Actions
 
 | Statement | Syntax | Notes |