feat: locale routing (en flat, zh subfolder), language switcher, dark default

- Derive lang from folder (posts/zh/* -> zh, else en); remove lang: frontmatter
- Change post route to [...slug] to capture nested zh paths
- Add nav language switcher (EN <-> 中文) + /zh/ landing page
- Default theme to dark (light opt-in via toggle)
- Translate hello-world-zh placeholder into English intro post
- Update case study: docker-compose sample + real install gotchas (commit history)
- Add docs/project-state.md (Tier 1/2/3 backlog)

src/content/posts/hello-world.md

@@ -0,0 +1,32 @@
+---
+title: "Hello, world — about this blog"
+description: "What this blog is for: technical writing, self-hosting experience, and a record of what I build and learn."
+pubDate: 2026-09-06
+category: notes
+tags: [intro]
+---
+
+Welcome. This is where I write about what I build and learn — mostly
+engineering, DevOps, and self-hosting, with some AI automation and Web3
+experiments mixed in.
+
+## What to expect
+
+English is the primary language here. I'll write selectively in Chinese
+(简体中文) for topics where a Chinese-speaking audience is better served —
+those posts will live under `/posts/zh/`.
+
+Most posts will be one of a few shapes:
+
+- **Case studies** — "how I built X", with the architecture and the mistakes.
+- **Tutorials** — a hard problem, what I tried, and the fix.
+- **Gotchas & notes** — short entries on the small things that cost me a day.
+
+## About me
+
+I'm Lee Teong Hoe (Mr Hoelee), a full-stack developer and DevOps engineer
+based in Malaysia. I build web applications, self-host a ~140-container
+homelab, and run an email-hosting business for Malaysian SMEs.
+
+If you're a recruiter, a client, or a fellow builder — the posts here are my
+living portfolio. Start with the [latest posts](/posts/).