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>

demos/use_cases/claude_code_router/README.md

@@ -1,6 +1,6 @@
 # Claude Code Router - Multi-Model Access with Intelligent Routing
 
-Arch Gateway extends Claude Code to access multiple LLM providers through a single interface. Offering two key benefits:
+Plano extends Claude Code to access multiple LLM providers through a single interface. Offering two key benefits:
 
 1. **Access to Models**: Connect to Grok, Mistral, Gemini, DeepSeek, GPT models, Claude, and local models via Ollama
 2. **Intelligent Routing via Preferences for Coding Tasks**: Configure which models handle specific development tasks:
@@ -21,15 +21,15 @@ Uses a [1.5B preference-aligned router LLM](https://arxiv.org/abs/2506.16655) to
 
 ## How It Works
 
-Arch Gateway sits between Claude Code and multiple LLM providers, analyzing each request to route it to the most suitable model:
+Plano sits between Claude Code and multiple LLM providers, analyzing each request to route it to the most suitable model:
 
 ```
-Your Request → Arch Gateway → Suitable Model → Response
+Your Request → Plano → Suitable Model → Response
              ↓
     [Task Analysis & Model Selection]
 ```
 
-**Supported Providers**: OpenAI-compatible, Anthropic, DeepSeek, Grok, Gemini, Llama, Mistral, local models via Ollama. See [full list of supported providers](https://docs.archgw.com/concepts/llm_providers/supported_providers.html).
+**Supported Providers**: OpenAI-compatible, Anthropic, DeepSeek, Grok, Gemini, Llama, Mistral, local models via Ollama. See [full list of supported providers](https://docs.planoai.dev/concepts/llm_providers/supported_providers.html).
 
 
 ## Quick Start (5 minutes)
@@ -61,7 +61,7 @@ export ANTHROPIC_API_KEY="your-anthropic-key-here"
 # Add other providers as needed
 ```
 
-### Step 3: Start Arch Gateway
+### Step 3: Start Plano
 ```bash
 # Install using uv (recommended)
 uv tool install planoai
@@ -122,7 +122,7 @@ planoai cli-agent claude --settings='{"ANTHROPIC_SMALL_FAST_MODEL": "deepseek-co
 ### Environment Variables
 The system automatically configures these variables for Claude Code:
 ```bash
-ANTHROPIC_BASE_URL=http://127.0.0.1:12000  # Routes through Arch Gateway
+ANTHROPIC_BASE_URL=http://127.0.0.1:12000  # Routes through Plano
 ANTHROPIC_SMALL_FAST_MODEL=arch.claude.code.small.fast    # Uses intelligent alias
 ```
 
@@ -147,6 +147,6 @@ llm_providers:
 
 ## Technical Details
 
-**How routing works:** Arch intercepts Claude Code requests, analyzes the content using preference-aligned routing, and forwards to the configured model.
+**How routing works:** Plano intercepts Claude Code requests, analyzes the content using preference-aligned routing, and forwards to the configured model.
 **Research foundation:** Built on our research in [Preference-Aligned LLM Routing](https://arxiv.org/abs/2506.16655)
-**Documentation:** [docs.archgw.com](https://docs.archgw.com) for advanced configuration and API details.
+**Documentation:** [docs.planoai.dev](https://docs.planoai.dev) for advanced configuration and API details.