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>

apps/www/src/lib/metadata.ts

@@ -115,7 +115,6 @@ export const siteConfig = {
     // Brand (minimal, necessary)
     "Plano AI",
     "Plano gateway",
-    "Arch gateway",
   ],
   authors: [{ name: "Katanemo", url: "https://github.com/katanemo/plano" }],
   creator: "Katanemo",
@@ -240,7 +239,7 @@ export const pageMetadata = {
       "agentic AI",
       "Plano blog",
       "Plano blog posts",
-      "Arch gateway blog",
+      "Plano gateway blog",
     ],
   }),