Release grok-build-hud v0.3.0: Claude-HUD-style same-window status for Grok Build

Multi-line tmux strip (context, quota, tools, todos, git), theme sync with
Grok UI, full/essential/minimal presets, one-shot installer, EN+ZH docs,
and 40 unit tests.

CONTRIBUTING.md

@@ -0,0 +1,37 @@
+# Contributing
+
+## Setup
+
+```bash
+git clone https://github.com/sooneocean/grok-build-hud.git
+cd grok-build-hud
+npm install
+npm test
+```
+
+## Layout
+
+| Path | Role |
+|------|------|
+| `src/` | TypeScript sources (session, billing, status, tmux, theme, CLI) |
+| `bin/` | CLI entrypoints (`grok-build-hud`, `grok-hud`, `grok-hud-run`, hook) |
+| `tests/` | Node built-in test runner (`node --test`) |
+| `fixtures/` | Session + billing samples for tests |
+| `commands/` / `skills/` | Grok plugin surface |
+| `scripts/install.sh` | One-shot local install |
+
+## Rules of thumb
+
+- Prefer reading **local** `~/.grok/sessions/**` over inventing APIs.
+- Billing must **degrade gracefully** when offline / unauthenticated (never throw in render path).
+- Keep the HUD **same-window** (tmux status). Do not require a second Terminal window by default.
+- Add or update a test when changing parse/normalize/render behaviour.
+- Commit messages in English; user-facing docs may be EN + ZH.
+
+## Before a PR
+
+```bash
+npm test
+```
+
+All 40 tests should pass.