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>

tests/e2e/common.py

@@ -98,17 +98,17 @@ def get_data_chunks(stream, n=1):
     return chunks
 
 
-def get_arch_messages(response_json):
-    arch_messages = []
+def get_plano_messages(response_json):
+    plano_messages = []
     if response_json and "metadata" in response_json:
-        # load arch_state from metadata
-        arch_state_str = response_json.get("metadata", {}).get(ARCH_STATE_HEADER, "{}")
-        # parse arch_state into json object
-        arch_state = json.loads(arch_state_str)
-        # load messages from arch_state
-        arch_messages_str = arch_state.get("messages", "[]")
+        # load plano_state from metadata
+        plano_state_str = response_json.get("metadata", {}).get(ARCH_STATE_HEADER, "{}")
+        # parse plano_state into json object
+        plano_state = json.loads(plano_state_str)
+        # load messages from plano_state
+        plano_messages_str = plano_state.get("messages", "[]")
         # parse messages into json object
-        arch_messages = json.loads(arch_messages_str)
-        # append messages from arch gateway to history
-        return arch_messages
+        plano_messages = json.loads(plano_messages_str)
+        # append messages from plano gateway to history
+        return plano_messages
     return []