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>

.gitignore

@@ -107,30 +107,30 @@ venv.bak/
 
 # =========================================
 
-# Arch
+# Plano
 cli/config
 cli/build
 
-# Archgw - Docs
+# Plano - Docs
 docs/build/
 
-# Archgw - Demos
+# Plano - Demos
 demos/function_calling/ollama/models/
 demos/function_calling/ollama/id_ed*
 demos/function_calling/open-webui/
 demos/function_calling/open-webui/
 demos/shared/signoz/data
 
-# Arch - Miscellaneous
+# Plano - Miscellaneous
 grafana-data
 prom_data
-arch_log/
-arch_logs/
+plano_log/
+plano_logs/
 crates/*/target/
 crates/target/
 build.log
 
-archgw.log
+plano.log
 
 # Next.js / Turborepo
 .next/