Rename all arch references to plano across the codebase

Complete rebrand from "Arch"/"archgw" to "Plano" including:
- Config files: arch_config_schema.yaml, workflow, demo configs
- Environment variables: ARCH_CONFIG_* → PLANO_CONFIG_*
- Python CLI: variables, functions, file paths, docker mounts
- Rust crates: config paths, log messages, metadata keys
- Docker/build: Dockerfile, supervisord, .dockerignore, .gitignore
- Docker Compose: volume mounts and env vars across all demos/tests
- GitHub workflows: job/step names
- Shell scripts: log messages
- Demos: Python code, READMEs, VS Code configs, Grafana dashboard
- Docs: RST includes, code comments, config references
- Package metadata: package.json, pyproject.toml, uv.lock

External URLs (docs.archgw.com, github.com/katanemo/archgw) left as-is.

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

crates/common/src/configuration.rs

@@ -493,7 +493,7 @@ mod test {
     #[test]
     fn test_deserialize_configuration() {
         let ref_config = fs::read_to_string(
-            "../../docs/source/resources/includes/arch_config_full_reference_rendered.yaml",
+            "../../docs/source/resources/includes/plano_config_full_reference_rendered.yaml",
         )
         .expect("reference config file not found");
 
@@ -520,7 +520,7 @@ mod test {
     #[test]
     fn test_tool_conversion() {
         let ref_config = fs::read_to_string(
-            "../../docs/source/resources/includes/arch_config_full_reference_rendered.yaml",
+            "../../docs/source/resources/includes/plano_config_full_reference_rendered.yaml",
         )
         .expect("reference config file not found");
         let config: super::Configuration = serde_yaml::from_str(&ref_config).unwrap();