Fix remaining arch references found in second pass

- config/docker-compose.dev.yaml: ARCH_CONFIG_FILE → PLANO_CONFIG_FILE,
  arch_config.yaml → plano_config.yaml, archgw_logs → plano_logs
- config/test_passthrough.yaml: container mount path
- tests/e2e/docker-compose.yaml: source file path (was still arch_config.yaml)
- cli/planoai/core.py: comment and log message
- crates/brightstaff/src/tracing/constants.rs: doc comment
- tests/{e2e,archgw}/common.py: get_arch_messages → get_plano_messages,
  arch_state/arch_messages variables renamed
- tests/{e2e,archgw}/test_prompt_gateway.py: updated imports and usages
- demos/shared/test_runner/{common,test_demos}.py: same renames
- tests/e2e/test_model_alias_routing.py: docstring
- .dockerignore: archgw_modelserver → plano_modelserver
- demos/use_cases/claude_code_router/pretty_model_resolution.sh: container name

Note: x-arch-* HTTP header values and Rust constant names intentionally
preserved for backwards compatibility with existing deployments.

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

cli/planoai/core.py

@@ -167,7 +167,7 @@ def start_cli_agent(plano_config_file=None, settings_json="{}"):
     env = os.environ.copy()
     env.update(
         {
-            "ANTHROPIC_AUTH_TOKEN": "test",  # Use test token for arch
+            "ANTHROPIC_AUTH_TOKEN": "test",  # Use test token for plano
             "ANTHROPIC_API_KEY": "",
             "ANTHROPIC_BASE_URL": f"http://{host}:{port}",
             "NO_PROXY": host,
@@ -220,7 +220,7 @@ def start_cli_agent(plano_config_file=None, settings_json="{}"):
 
     # Use claude from PATH
     claude_path = "claude"
-    log.info(f"Connecting Claude Code Agent to Arch at {host}:{port}")
+    log.info(f"Connecting Claude Code Agent to Plano at {host}:{port}")
 
     try:
         subprocess.run([claude_path] + claude_args, env=env, check=True)