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/installation.en.md

@@ -13,7 +13,7 @@ description: Install PenguinHarness via the install script, npm, or from source.
 On 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
 ```
 
 The script downloads the matching `penguin-{linux,darwin}-{x64,arm64}.tar.gz`, which bundles an official Node.js runtime. Other platforms do **not** fall back automatically: the script exits and asks you to install Node.js >= 24 and re-run with `--universal`, which selects the runtime-less `penguin-universal.tar.gz`.
@@ -34,7 +34,7 @@ penguin -v
 | Integrity check | Downloads are sha256-verified when the Release ships checksum assets |
 | Upgrade | Re-run the install script; files are swapped atomically |
 
-Script flags are passed as `curl ... | sh -s -- --universal`.
+Script flags go after `sh -s --`, e.g. `curl -fsSL https://penguin.ooo/install.sh | sh -s -- --universal`.
 
 ### Data directory