refactor: organize API routers and services into subpackages

Service organization (19 files moved into 6 subpackages):
- services/instance/ — event_bus, health_monitor, lifecycle_hooks
- services/config/ — config_profile_resolver
- services/git/ — clone, git_operations, git_service
- services/build/ — docker_build, manifest_compiler
- services/terminal/ — terminal_manager, terminal_session
- services/shared/ — correlation, file_service, notification_service,
  permission_fixer, readiness_probe, ssh_keys, tunnel, workspace_manager

API router organization (16 files moved into 6 subpackages):
- api/tool/ — tool_instances, tool_types, tool_definitions,
  tool_types_validation, sessions (extracted from tool_instances)
- api/config/ — config_profiles, user_config
- api/workspace/ — workspaces, workspace_files, workspace_git,
  workspace_instances
- api/user/ — users, auth, ssh_keys
- api/project/ — projects, git_repositories
- api/system/ — health, events, notifications, dashboard, terminal,
  instance_proxy

Updated main.py imports and all __init__.py re-exports.
Sessions router extracted from tool_instances.py into api/tool/sessions.py.

Quality gates: py_compile passed, ruff passed.

apps/api/src/services/shared/readiness_probe.py

@@ -0,0 +1,66 @@
+"""Readiness probe service for checking if containers are ready."""
+
+import asyncio
+import logging
+import subprocess
+
+logger = logging.getLogger(__name__)
+
+
+async def execute_probe(
+    container_id: str,
+    command: str,
+    timeout: int = 30,
+    interval: int = 2,
+) -> tuple[bool, list[str]]:
+    """Execute a readiness probe command inside a container.
+
+    Args:
+        container_id: Docker container ID or name
+        command: Command to execute inside the container
+        timeout: Maximum total time to wait (seconds)
+        interval: Time between retries (seconds)
+
+    Returns:
+        Tuple of (success, logs)
+    """
+    logs = []
+    start_time = asyncio.get_event_loop().time()
+    attempt = 0
+
+    while True:
+        attempt += 1
+        elapsed = asyncio.get_event_loop().time() - start_time
+        
+        if elapsed >= timeout:
+            logs.append(f"Probe timed out after {timeout}s ({attempt} attempts)")
+            return False, logs
+
+        try:
+            logger.debug("Probe attempt %d: %s", attempt, command)
+            
+            # Execute command inside container
+            result = subprocess.run(
+                ["docker", "exec", container_id, "sh", "-c", command],
+                capture_output=True,
+                text=True,
+                timeout=interval,  # Each attempt has its own timeout
+            )
+            
+            if result.returncode == 0:
+                logs.append(f"Attempt {attempt}: Success")
+                if result.stdout:
+                    logs.append(f"Output: {result.stdout.strip()}")
+                return True, logs
+            else:
+                logs.append(f"Attempt {attempt}: Failed (exit code {result.returncode})")
+                if result.stderr:
+                    logs.append(f"Stderr: {result.stderr.strip()[:200]}")
+                
+        except subprocess.TimeoutExpired:
+            logs.append(f"Attempt {attempt}: Command timed out")
+        except Exception as exc:
+            logs.append(f"Attempt {attempt}: Error - {exc}")
+
+        # Wait before next attempt
+        await asyncio.sleep(interval)