Refactor config_generator into modular, testable components

Break the 507-line monolithic validate_and_render_schema() into focused
modules with pure validation functions, proper error handling, and clean
I/O separation:

- config_providers.py: provider constants, ConfigValidationError, unified
  URL parsing (replaces 3 different inline implementations)
- config_validator.py: 11 pure validation functions (no I/O, no print/exit)
- config_generator.py: thin 146-line I/O orchestrator, reads files once
  (was twice), uses logging instead of print()

Also cleans up module responsibilities:
- Move stream_access_logs from utils.py to docker_cli.py (Docker operation)
- Deduplicate llm_providers->model_providers migration
- Fix "Model alias 2 -" debug artifact in error message
- Update docker-compose.dev.yaml volume mounts for new files
- Rewrite tests: 53 tests calling pure functions directly (no mock_open
  chains), up from 10 brittle mock-dependent tests

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cli/planoai/docker_cli.py

@@ -115,6 +115,28 @@ def stream_gateway_logs(follow, service="plano"):
         log.info(f"Failed to stream logs: {str(e)}")
 
 
+def stream_access_logs(follow):
+    """Stream access logs from the running Plano container."""
+
+    follow_arg = "-f" if follow else ""
+
+    stream_command = [
+        "docker",
+        "exec",
+        PLANO_DOCKER_NAME,
+        "sh",
+        "-c",
+        f"tail {follow_arg} /var/log/access_*.log",
+    ]
+
+    subprocess.run(
+        stream_command,
+        check=True,
+        stdout=sys.stdout,
+        stderr=sys.stderr,
+    )
+
+
 def docker_validate_plano_schema(arch_config_file):
     import os