Changelog, dev startup, README, AgentHub 0.4.0, model catalog, and landing site (#7)

Branch-length batch covering tooling, the model layer, the Web App and the public
surfaces. Highlights:

- Changelog: a per-release `changelog/<version>/` tree, grouped by the surface each
  change touches, with a root CHANGELOG.md holding one line per release.
- Dev startup: `scripts/dev-prebuild.mjs` serializes the skills+core prebuild behind a
  lock and keeps `pnpm install` current; `pnpm dev` runs server+web together.
- AgentHub 0.3.3 -> 0.4.0: OmniMessage complete payloads carry one opaque `fidelity`
  object in place of item-level `signature`/`phase`, threaded verbatim through Trace,
  replay and resume; malformed classification adapted to the new error types.
- Model layer: a model is always referenced by an explicit `(provider, model_id)` pair.
  The provider is never inferred, guessed or defaulted -- both the catalog inference and
  the unique-match config resolution are gone, and CLI, SDK, server routes and
  run_subagent all require the complete pair. Catalog gains the Qwen Token Plan, Qwen
  Pay-As-You-Go and Fireworks AI gateways, plus an expanded OpenRouter group.
- Web App: catalog preset sync and per-group speed test on the Models page, positional
  slash commands, a markdown renderer, skill-library update reminders, and a vertically
  centred draft page whose upward menus size themselves to the room available.
- Public surfaces: restructured READMEs, the penguin.ooo landing site and blog, refreshed
  benchmark results for both suites, and the demo videos playing on the landing page.

Includes the fixes from a full review of the branch: 23 confirmed findings, among them a
provider-inference bug that could send one vendor's API key to another vendor's endpoint,
and an Escape handler that destroyed the composer's contents unrecoverably.

Verified on the branch head: pnpm test (1127 passing, 7 packages), pnpm typecheck and
pnpm format:check clean, Playwright e2e 14/14.

packages/docs/content/quickstart.zh.md

@@ -8,7 +8,7 @@ description: 安装 PenguinHarness、配置模型并运行第一个 Task。
 Linux / macOS 一键安装：
 
 ```bash
-curl -fsSL https://github.com/Prism-Shadow/penguin-harness/releases/latest/download/install.sh | sh
+curl -fsSL https://penguin.ooo/install.sh | sh
 ```
 
 其他方式（npm、源码）见[安装](/installation)。
@@ -18,10 +18,10 @@ curl -fsSL https://github.com/Prism-Shadow/penguin-harness/releases/latest/downl
 PenguinHarness 不内置任何模型凭据，使用前需要先配置一个模型。可以在 Web UI 的 Models 页面完成，也可以用 CLI：
 
 ```bash
-penguin config model add --model-id deepseek-v4-pro --api-key sk-... --set-default
+penguin config model add --provider deepseek --model-id deepseek-v4-pro --api-key sk-... --set-default
 ```
 
-- 省略 `--provider` 时，根据内置目录自动推断 Provider。
+- 模型引用始终是 `(provider, model_id)` 二元组，因此 `--provider` 与 `--model-id` 均为必填——Provider 绝不由模型 id 推断。内置分组见[模型与 Provider](/models)。
 - API Key 也可以来自环境变量：当模型条目没有内联 api_key 时，LLM 网关库 AgentHub 会读取 `DEEPSEEK_API_KEY`、`ANTHROPIC_API_KEY`、`OPENAI_API_KEY`、`GEMINI_API_KEY` 等变量；工作目录下的 `.env` 会被自动加载。
 
 ## 启动 Web App
@@ -30,7 +30,7 @@ penguin config model add --model-id deepseek-v4-pro --api-key sk-... --set-defau
 penguin web
 ```
 
-服务运行在 http://127.0.0.1:7364 并自动打开浏览器（`--no-open` 跳过）。首次登录使用 `admin` / `admin123`，请立即修改密码。`penguin server` 启动同一进程的 headless 版本。
+服务运行在 http://127.0.0.1:7364 并自动打开浏览器（`--no-open` 跳过）。首次登录使用 `admin` / `penguin-2026`，请立即修改密码。`penguin server` 启动同一进程的 headless 版本。
 
 ## 单次运行