Rename all arch references to plano (#745)

* 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>

* Update remaining arch references in docs

- Rename RST cross-reference labels: arch_access_logging, arch_overview_tracing, arch_overview_threading → plano_*
- Update label references in request_lifecycle.rst
- Rename arch_config_state_storage_example.yaml → plano_config_state_storage_example.yaml
- Update config YAML comments: "Arch creates/uses" → "Plano creates/uses"
- Update "the Arch gateway" → "the Plano gateway" in configuration_reference.rst
- Update arch_config_schema.yaml reference in provider_models.py
- Rename arch_agent_router → plano_agent_router in config example

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

* 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>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

crates/brightstaff/src/tracing/constants.rs

@@ -182,7 +182,7 @@ pub mod signals {
 // Operation Names
 // =============================================================================
 
-/// Canonical operation name components for Arch Gateway
+/// Canonical operation name components for Plano Gateway
 pub mod operation_component {
     /// Inbound request handling
     pub const INBOUND: &str = "plano(inbound)";
@@ -210,7 +210,7 @@ pub mod operation_component {
 ///
 /// Format: `{method} {path} {target}`
 ///
-/// The operation component (e.g., "archgw(llm)") is now part of the service name,
+/// The operation component (e.g., "plano(llm)") is now part of the service name,
 /// so the operation name focuses on the HTTP request details and target.
 ///
 /// # Examples
@@ -218,7 +218,7 @@ pub mod operation_component {
 /// use brightstaff::tracing::OperationNameBuilder;
 ///
 /// // LLM call operation: "POST /v1/chat/completions gpt-4"
-/// // (service name will be "archgw(llm)")
+/// // (service name will be "plano(llm)")
 /// let op = OperationNameBuilder::new()
 ///     .with_method("POST")
 ///     .with_path("/v1/chat/completions")
@@ -226,7 +226,7 @@ pub mod operation_component {
 ///     .build();
 ///
 /// // Agent filter operation: "POST /agents/v1/chat/completions hallucination-detector"
-/// // (service name will be "archgw(agent filter)")
+/// // (service name will be "plano(agent filter)")
 /// let op = OperationNameBuilder::new()
 ///     .with_method("POST")
 ///     .with_path("/agents/v1/chat/completions")
@@ -234,7 +234,7 @@ pub mod operation_component {
 ///     .build();
 ///
 /// // Routing operation: "POST /v1/chat/completions"
-/// // (service name will be "archgw(routing)")
+/// // (service name will be "plano(routing)")
 /// let op = OperationNameBuilder::new()
 ///     .with_method("POST")
 ///     .with_path("/v1/chat/completions")