* fix(ui): resolve eslint errors surfaced by dep bumps
Clear the 6 eslint errors introduced by the typescript-eslint / TS 6.0
dependency bumps:
- sidebarPrefs.ts, vite.config.ts: inline type imports -> top-level
type-only imports; sort import members (autofix)
- cloud-agents.tsx: drop optional chain on session.data (already
narrowed non-null by the earlier login guard)
- vite.config.ts: drop optional chain on proxyHead (typed Buffer from
the upgrade event, always present)
No behavior change. eslint and tsc --noEmit both clean.
* docs(env): track .env.example and document deployment vars
- Un-ignore .env.example (!.env.example) so the template stays tracked;
.env / .env.* secret files remain ignored.
- Add LLM_MODEL_ID, AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY (used by the
Bedrock/managed deployment but previously undocumented).
- Mark LANGCHAIN_TRACING_V2 and LANGCHAIN_PROJECT as reserved on
LangGraph Platform (the platform sets them; deploys are rejected if
provided).
