feat: implement Strategy Pattern fragmentation with optional parsers

- Add TreeSitterStrategy for 9 languages (Python, JS, TS, Go, Rust, Java, C, C++, Ruby)
- Add PythonAstStrategy as stdlib fallback
- Add MistuneMarkdownStrategy and RegexMarkdownStrategy for Markdown
- Add HTMLStrategy with lxml for HTML/XML semantic blocks
- Add RuamelYamlStrategy for YAML with position tracking
- Add PySBDTextStrategy for sentence-aware text splitting
- Add ConfigStrategy, ParagraphStrategy, GenericStrategy fallbacks
- Add FragmentationEngine with priority-based chain of responsibility
- All parsers are optional with graceful degradation

Author: nikolay-e

.github/workflows/ci.yml

@@ -60,9 +60,9 @@ jobs:
         uses: actions/cache@v5
         with:
           path: ~/.cache/pip
-          key: ${{ runner.os }}-lint-pip-${{ hashFiles('**/pyproject.toml') }}
+          key: ${{ runner.os }}-lint-pip-3.11-${{ hashFiles('**/pyproject.toml') }}
           restore-keys: |
-            ${{ runner.os }}-lint-pip-
+            ${{ runner.os }}-lint-pip-3.11-
 
       - name: Install Linters and Type Checker
         run: |
@@ -121,9 +121,8 @@ jobs:
             --cov-report=term-missing --cov-branch --junitxml=test-results.xml
 
       - name: Coverage report with threshold
-        if: runner.os == 'Linux' && matrix.python-version == '3.12'
         run: |
-          coverage report --fail-under=80 --skip-covered --show-missing
+          coverage report --fail-under=80
 
       - name: Upload coverage reports to Codecov
         if: runner.os == 'Linux' && matrix.python-version == '3.12'
@@ -177,11 +176,10 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install -e .
-          pip install pytest pytest-cov
+          pip install pytest
 
       - name: Run Tests
-        run: |
-          pytest -v
+        run: pytest -v
 
   # ============================================================================
   # Mutation Testing (test effectiveness validation)
@@ -210,9 +208,8 @@ jobs:
 
       - name: Run mutation testing
         run: |
-          mutmut run . || true
+          mutmut run --paths-to-mutate=src/treemapper/ --tests-dir=tests/ || true
           mutmut results || true
-        continue-on-error: true
 
   # ============================================================================
   # Complexity & Maintainability Metrics
@@ -297,7 +294,6 @@ jobs:
 
       - name: Check import contracts
         run: lint-imports
-        continue-on-error: true
 
   # ============================================================================
   # SonarCloud Quality Gate
@@ -344,4 +340,3 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}
-        continue-on-error: true