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/server/test/schedule-file.test.ts

@@ -49,6 +49,11 @@ describe("parseScheduleFile", () => {
     });
   });
 
+  it("keeps a complete model reference pair", () => {
+    const def = defOf(`${BASE}provider = "custom"\nmodel_id = "m1"\n`);
+    expect(def).toMatchObject({ provider: "custom", modelId: "m1" });
+  });
+
   it("enabled defaults to off; omitting period means one-shot", () => {
     const def = defOf(`prompt = "p"\nstart_at = "2026-07-16T09:00:00Z"\n`);
     expect(def.enabled).toBe(false);
@@ -67,6 +72,10 @@ describe("parseScheduleFile", () => {
       [`${BASE}session_id = "s"\nworkspace = "/tmp/w"\n`, "new-Session mode"],
       [`${BASE}session_id = "s"\nmodel_id = "m1"\n`, "new-Session mode"],
       [`${BASE}model_id = ""\n`, "model_id"],
+      // A model reference is always a pair: half of one is invalid in either direction
+      // (model_id alone is what a file written before this rule looks like).
+      [`${BASE}model_id = "m1"\n`, "given together"],
+      [`${BASE}provider = "custom"\n`, "given together"],
     ];
     for (const [raw, hint] of cases) {
       const r = parseScheduleFile("x", raw);