chore: drop HOST overrides, move known issue to docs, tidy comments and gitignores

- Remove HOST=${SERVICE_HOSTNAME} from code-server, code-server-lsio and paseo; hostname: alone sets the name
- Move SERVICE_HOSTNAME to the top of their .env.example to match compose order
- Drop the openclaw ARM64 Chromium note from its README; docs/openclaw covers it
- List CUSTOM_USER in webtop's setup step
- Trim reasoning from diun and paseo comments
- Delete stale gitea and gitea-mirror .gitignore files
- Add TODO.md for remaining naming and README issues

CLAUDE.md

@@ -151,7 +151,7 @@ collapse and the existing grouping stands.
 
 `.env.example` follows its compose file's order. The names differ — one
 `PASSWORD` can feed several container variables, and `SERVICE_HOSTNAME` feeds
-`HOST` — so each entry sits where the first compose entry that reads it sits.
+`hostname:` — so each entry sits where the first compose entry that reads it sits.
 Reordering a compose file means reordering the `.env.example` with it.
 
 ## Deployment target