feat(#154): Implement context estimator

Implements formula-based context estimation for predicting token
usage before issue assignment.

Formula:
  base = (files × 7000) + complexity + tests + docs
  total = base × 1.3  (30% safety buffer)

Features:
- EstimationInput/Result data models with validation
- ComplexityLevel, TestLevel, DocLevel enums
- Agent recommendation (haiku/sonnet/opus) based on tokens
- Validation against actual usage with tolerance checking
- Convenience function for quick estimations
- JSON serialization support

Implementation:
- issue_estimator.py: Core estimator with formula
- models.py: Data models and enums (100% coverage)
- test_issue_estimator.py: 35 tests, 100% coverage
- ESTIMATOR.md: Complete API documentation
- requirements.txt: Python dependencies
- .coveragerc: Coverage configuration

Test Results:
- 35 tests passing
- 100% code coverage (excluding __main__)
- Validates against historical issues
- All edge cases covered

Acceptance Criteria Met:
✅ Context estimation formula implemented
✅ Validation suite tests against historical issues
✅ Formula includes all components (files, complexity, tests, docs, buffer)
✅ Unit tests for estimator (100% coverage, exceeds 85% requirement)
✅ All components tested (low/medium/high levels)
✅ Agent recommendation logic validated

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

scripts/coordinator/README.md

@@ -8,7 +8,59 @@ The coordinator system automates issue assignment, tracking, and orchestration a
 
 ## Scripts
 
-### create-gitea-bot.sh
+### Python Modules
+
+#### issue_estimator.py
+
+Formula-based context estimator for predicting token usage before issue assignment.
+
+**Prerequisites:**
+
+- Python 3.8+
+- Virtual environment with dependencies (see Installation below)
+
+**Usage:**
+
+```bash
+# Create virtual environment
+python3 -m venv venv
+source venv/bin/activate  # Windows: venv\Scripts\activate
+
+# Install dependencies
+pip install -r requirements.txt
+
+# Run examples
+python issue_estimator.py
+
+# Run tests
+pytest test_issue_estimator.py -v
+
+# Run with coverage
+pytest test_issue_estimator.py --cov=issue_estimator --cov=models --cov-report=term-missing
+```
+
+**Python API:**
+
+```python
+from issue_estimator import estimate_issue
+
+# Quick estimation
+result = estimate_issue(
+    files=2,
+    complexity="medium",
+    tests="medium",
+    docs="light"
+)
+
+print(f"Total estimate: {result.total_estimate:,} tokens")
+print(f"Recommended agent: {result.recommended_agent}")
+```
+
+**Documentation:** See [ESTIMATOR.md](ESTIMATOR.md) for complete API reference and examples.
+
+### Bash Scripts
+
+#### create-gitea-bot.sh
 
 Creates the `mosaic` bot user in Gitea for coordinator automation.
 
@@ -79,6 +131,37 @@ export TEST_ISSUE="156"
 **Output:**
 Success/failure for each test with detailed error messages.
 
+## Installation
+
+### Python Environment
+
+For the context estimator and Python-based coordinator components:
+
+```bash
+# Navigate to coordinator directory
+cd scripts/coordinator
+
+# Create virtual environment
+python3 -m venv venv
+
+# Activate virtual environment
+source venv/bin/activate  # Windows: venv\Scripts\activate
+
+# Install dependencies
+pip install -r requirements.txt
+
+# Verify installation
+pytest test_issue_estimator.py -v
+```
+
+### Bash Scripts
+
+No installation needed for bash scripts. Just ensure they're executable:
+
+```bash
+chmod +x scripts/coordinator/*.sh
+```
+
 ## Configuration
 
 ### Environment Variables
@@ -258,9 +341,24 @@ For complete documentation on the coordinator bot:
 - [Issue #156 - Create coordinator bot user](https://git.mosaicstack.dev/mosaic/stack/issues/156)
 - [Coordinator Architecture](../../docs/3-architecture/non-ai-coordinator-comprehensive.md)
 
+## Files
+
+| File                      | Purpose                              |
+| ------------------------- | ------------------------------------ |
+| `issue_estimator.py`      | Context estimator implementation     |
+| `models.py`               | Data models and enums for estimator  |
+| `test_issue_estimator.py` | Test suite (35 tests, 100% coverage) |
+| `ESTIMATOR.md`            | Complete estimator documentation     |
+| `requirements.txt`        | Python dependencies                  |
+| `.coveragerc`             | Coverage configuration               |
+| `create-gitea-bot.sh`     | Bot user creation script             |
+| `test-gitea-bot.sh`       | Bot functionality tests              |
+| `README.md`               | This file                            |
+
 ## Related Issues
 
-- #156 - Create coordinator bot user in Gitea
+- #154 - Implement context estimator ✅ **COMPLETED**
+- #156 - Create coordinator bot user in Gitea ✅ **COMPLETED**
 - #157 - Configure coordinator webhook in Gitea
 - #158 - Implement coordinator task assignment engine
 - #140 - Coordinator integration architecture