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.en.md

@@ -8,7 +8,7 @@ description: Install PenguinHarness, configure a model, and run your first Task.
 One-liner for Linux / macOS:
 
 ```bash
-curl -fsSL https://github.com/Prism-Shadow/penguin-harness/releases/latest/download/install.sh | sh
+curl -fsSL https://penguin.ooo/install.sh | sh
 ```
 
 For other options (npm, from source), see [Installation](/installation).
@@ -18,10 +18,10 @@ For other options (npm, from source), see [Installation](/installation).
 PenguinHarness ships with no built-in model credentials, so configure a model first. Use the Models page in the Web UI, or the 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
 ```
 
-- When `--provider` is omitted, the Provider is inferred from the built-in catalog.
+- A model is always referenced as a `(provider, model_id)` pair, so `--provider` and `--model-id` are both required — the Provider is never inferred from the model id. See [Models & Providers](/models) for the built-in groups.
 - The API key can also come from environment variables: when a model entry has no inline api_key, AgentHub (the LLM gateway library) reads variables such as `DEEPSEEK_API_KEY`, `ANTHROPIC_API_KEY`, `OPENAI_API_KEY`, and `GEMINI_API_KEY`. A `.env` file in the working directory is loaded automatically.
 
 ## Start the Web App
@@ -30,7 +30,7 @@ penguin config model add --model-id deepseek-v4-pro --api-key sk-... --set-defau
 penguin web
 ```
 
-The service runs at http://127.0.0.1:7364 and opens your browser (`--no-open` to skip). First login is `admin` / `admin123` — change it right away. `penguin server` starts the same process headless.
+The service runs at http://127.0.0.1:7364 and opens your browser (`--no-open` to skip). First login is `admin` / `penguin-2026` — change it right away. `penguin server` starts the same process headless.
 
 ## One-shot run