feat(#160): Implement basic orchestration loop

Implements the Coordinator class with main orchestration loop:
- Async loop architecture with configurable poll interval
- process_queue() method gets next ready issue and spawns agent (stub)
- Graceful shutdown handling with stop() method
- Error handling that allows loop to continue after failures
- Logging for all actions (start, stop, processing, errors)
- Integration with QueueManager from #159
- Active agent tracking for future agent management

Configuration settings added:
- COORDINATOR_POLL_INTERVAL (default: 5.0s)
- COORDINATOR_MAX_CONCURRENT_AGENTS (default: 10)
- COORDINATOR_ENABLED (default: true)

Tests: 27 new tests covering all acceptance criteria
Coverage: 92% overall (100% for coordinator.py)

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

apps/coordinator/tests/test_parser.py

@@ -1,13 +1,12 @@
 """Tests for issue parser agent."""
 
-import os
+from unittest.mock import Mock, patch
+
 import pytest
-from unittest.mock import Mock, patch, AsyncMock
 from anthropic import Anthropic
 from anthropic.types import Message, TextBlock, Usage
 
-from src.parser import parse_issue_metadata, clear_cache
-from src.models import IssueMetadata
+from src.parser import clear_cache, parse_issue_metadata
 
 
 @pytest.fixture(autouse=True)
@@ -88,7 +87,10 @@ def mock_anthropic_response() -> Message:
         content=[
             TextBlock(
                 type="text",
-                text='{"estimated_context": 46800, "difficulty": "medium", "assigned_agent": "sonnet", "blocks": [159], "blocked_by": [157]}'
+                text=(
+                    '{"estimated_context": 46800, "difficulty": "medium", '
+                    '"assigned_agent": "sonnet", "blocks": [159], "blocked_by": [157]}'
+                ),
             )
         ],
         model="claude-sonnet-4.5-20250929",
@@ -107,7 +109,10 @@ def mock_anthropic_minimal_response() -> Message:
         content=[
             TextBlock(
                 type="text",
-                text='{"estimated_context": 50000, "difficulty": "medium", "assigned_agent": "sonnet", "blocks": [], "blocked_by": []}'
+                text=(
+                    '{"estimated_context": 50000, "difficulty": "medium", '
+                    '"assigned_agent": "sonnet", "blocks": [], "blocked_by": []}'
+                ),
             )
         ],
         model="claude-sonnet-4.5-20250929",
@@ -306,7 +311,10 @@ class TestParseIssueMetadata:
                 content=[
                     TextBlock(
                         type="text",
-                        text='{"estimated_context": 10000, "difficulty": "invalid", "assigned_agent": "sonnet", "blocks": [], "blocked_by": []}'
+                        text=(
+                            '{"estimated_context": 10000, "difficulty": "invalid", '
+                            '"assigned_agent": "sonnet", "blocks": [], "blocked_by": []}'
+                        ),
                     )
                 ],
                 model="claude-sonnet-4.5-20250929",
@@ -341,7 +349,10 @@ class TestParseIssueMetadata:
                 content=[
                     TextBlock(
                         type="text",
-                        text='{"estimated_context": 10000, "difficulty": "medium", "assigned_agent": "invalid_agent", "blocks": [], "blocked_by": []}'
+                        text=(
+                            '{"estimated_context": 10000, "difficulty": "medium", '
+                            '"assigned_agent": "invalid_agent", "blocks": [], "blocked_by": []}'
+                        ),
                     )
                 ],
                 model="claude-sonnet-4.5-20250929",