[gemma4] refactor using treesitter

PLAN.md

@@ -15,19 +15,18 @@ This document outlines the identified fragilities in the `skillls` project and t
 **Proposed Actions**:
 - [x] Refactor `SkillParser._traverse_tree` to use an iterative approach (using a stack/deque) instead of recursion.
 
-## s3. Single Source of Truth for Errors
+## 3. Single Source of Truth for Errors
 **Problem**: The project is in a transitional state where error management is split between the new `SkillParser` diagnostics and the legacy `server.errs` dictionary in `main.py`.
 **Goal**: Unify error reporting into a single, streamlined pipeline.
 **Proposed Actions**:
-- [ ] Complete the refactor of `skillls/main.py`.
-- [ ] Remove the `errs` dictionary from `SkillLanguageServer`.
-- [ ] Decommission and delete deprecated files: `skillls/checker.py` and unused parts of `skillls/helpers.py`.
+- [x] Complete the refactor of `skillls/main.py`.
+- [x] Remove the `errs` dictionary from `SkillLanguageServer`.
+- [x] Decommission and delete deprecated files: `skillls/checker.py` and unused parts of `skillls/helpers.py`.
 
 
 ## 5. Test Suite Strengthening
 **Problem**: While core logic is tested, the LSP lifecycle and complex parsing edge cases lack specific unit test coverage.
 **Goal**: Achieve high-confidence verification of the LSP server's behavior and parser robustness.
 **Proposed Actions**:
-- [ ] Implement `tests/test_server.py` to verify LSP lifecycle events (`didOpen`, `didChange`) and diagnostic publishing logic.
-- [ ] Expand `tests/test_helpers.py` with specialized unit tests for the `find_scopes` regex and brace-tracking logic.
-- [ ] Harden `tests/test_parser.py` by implementing deterministic symbol extraction verification instead of existence checks.
+- [x] Implement \`tests/test_server.py\` to verify LSP lifecycle events (\`didOpen\`, \`didChange\`) and diagnostic publishing logic.
+- [x] Harden `tests/test_parser.py` by implementing deterministic symbol extraction verification instead of existence checks.