docs: clarify generated grammar files are not committed to git

Update the PR checklist and ANTLR4 section to reflect that
`mdl/grammar/parser/` is regenerated by `make grammar` at build time
and must not be committed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ako

CLAUDE.md

@@ -282,7 +282,7 @@ All executor code must go through the backend abstraction layer — the executor
 ### Full-stack consistency for MDL features
 New MDL commands or language features must be wired through the full pipeline:
 - [ ] **Grammar** — rule added to `MDLParser.g4` (and `MDLLexer.g4` if new tokens)
-- [ ] **Parser regenerated** — `make grammar` run, generated files committed
+- [ ] **Parser regenerated** — `make grammar` run; generated files in `mdl/grammar/parser/` are **not** committed (they are regenerated by `make` at build time)
 - [ ] **AST** — node type added in `mdl/ast/`
 - [ ] **Visitor** — ANTLR listener bridges parse tree to AST in `mdl/visitor/`
 - [ ] **Executor** — thin handler in `mdl/executor/` dispatches to `ctx.Backend.*`; no BSON in the handler
@@ -418,7 +418,7 @@ The `vscode-mdl` extension provides MDL language support: syntax highlighting, p
 
 ### ANTLR4 Parser
 
-Regenerate after modifying `MDLLexer.g4` or `MDLParser.g4`: `make grammar`. See `docs/03-development/MDL_PARSER_ARCHITECTURE.md` for design details.
+Regenerate after modifying `MDLLexer.g4`, `MDLParser.g4`, or any `domains/*.g4` file: `make grammar`. Generated files in `mdl/grammar/parser/` are **not** committed to git. See `docs/03-development/MDL_PARSER_ARCHITECTURE.md` for design details.
 
 ## IMPORTANT: Before Writing MDL Scripts or Working with Data