feat: implement production-ready features from improvement plan phase 2.5 & 2.6

Phase 2.5: Fix Foundation (CRITICAL)
- Fixed 4 failing tests by adding cache attribute to mock_client fixture
- Created comprehensive cache tests for Pages endpoint (test_pages_cache.py)
- Added missing dependencies: pydantic[email] and aiohttp to core requirements
- Updated requirements.txt with proper dependency versions
- Achieved 82.67% test coverage with 454 passing tests

Phase 2.6: Production Essentials
- Implemented structured logging (wikijs/logging.py)
  * JSON and text log formatters
  * Configurable log levels and output destinations
  * Integration with client operations

- Implemented metrics and telemetry (wikijs/metrics.py)
  * Request tracking with duration, status codes, errors
  * Latency percentiles (min, max, avg, p50, p95, p99)
  * Error rate calculation
  * Thread-safe metrics collection

- Implemented rate limiting (wikijs/ratelimit.py)
  * Token bucket algorithm for request throttling
  * Per-endpoint rate limiting support
  * Configurable timeout handling
  * Burst capacity management

- Created SECURITY.md policy
  * Vulnerability reporting procedures
  * Security best practices
  * Response timelines
  * Supported versions

Documentation
- Added comprehensive logging guide (docs/logging.md)
- Added metrics and telemetry guide (docs/metrics.md)
- Added rate limiting guide (docs/rate_limiting.md)
- Updated README.md with production features section
- Updated IMPROVEMENT_PLAN_2.md with completed checkboxes

Testing
- Created test suite for logging (tests/test_logging.py)
- Created test suite for metrics (tests/test_metrics.py)
- Created test suite for rate limiting (tests/test_ratelimit.py)
- All 454 tests passing
- Test coverage: 82.67%

Breaking Changes: None
Dependencies Added: pydantic[email], email-validator, dnspython

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/test_logging.py

@@ -0,0 +1,41 @@
+"""Tests for logging functionality."""
+import logging
+import json
+from wikijs.logging import setup_logging, JSONFormatter
+
+
+def test_json_formatter():
+    """Test JSON log formatting."""
+    formatter = JSONFormatter()
+    record = logging.LogRecord(
+        name="test",
+        level=logging.INFO,
+        pathname="test.py",
+        lineno=10,
+        msg="Test message",
+        args=(),
+        exc_info=None
+    )
+
+    output = formatter.format(record)
+    log_data = json.loads(output)
+
+    assert log_data["level"] == "INFO"
+    assert log_data["message"] == "Test message"
+    assert "timestamp" in log_data
+
+
+def test_setup_logging_json():
+    """Test JSON logging setup."""
+    logger = setup_logging(level=logging.DEBUG, format_type="json")
+
+    assert logger.level == logging.DEBUG
+    assert len(logger.handlers) == 1
+
+
+def test_setup_logging_text():
+    """Test text logging setup."""
+    logger = setup_logging(level=logging.INFO, format_type="text")
+
+    assert logger.level == logging.INFO
+    assert len(logger.handlers) == 1