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/core/src/state/default-config.ts

@@ -28,6 +28,8 @@ export const SESSION_ID_PLACEHOLDER = "{{SESSION_ID}}";
 export const CWD_PLACEHOLDER = "{{CWD}}";
 export const AGENT_ID_PLACEHOLDER = "{{AGENT_ID}}";
 export const PROJECT_DIR_PLACEHOLDER = "{{PROJECT_DIR}}";
+export const PROVIDER_PLACEHOLDER = "{{PROVIDER}}";
+export const MODEL_ID_PLACEHOLDER = "{{MODEL_ID}}";
 export const PLATFORM_PLACEHOLDER = "{{PLATFORM}}";
 export const OS_VERSION_PLACEHOLDER = "{{OS_VERSION}}";
 export const DATE_PLACEHOLDER = "{{DATE}}";
@@ -141,9 +143,11 @@ Skills are reusable instruction packages stored under <project_dir>/agents/<agen
 - Platform: {{PLATFORM}}
 - OS Version: {{OS_VERSION}}
 - Date: {{DATE}}
-- CWD: {{CWD}}
-- Agent ID: {{AGENT_ID}}
 - Project Dir: {{PROJECT_DIR}}
+- Agent ID: {{AGENT_ID}}
+- CWD: {{CWD}}
+- Provider: {{PROVIDER}}
+- Model ID: {{MODEL_ID}}
 - Session ID: {{SESSION_ID}}`;
 
 /**
@@ -247,7 +251,12 @@ function defaultBuiltinTools(): ToolDefinitionConfig[] {
           model_id: {
             type: "string",
             description:
-              "Which model the subagent should use; defaults to the Project default model when omitted.",
+              "Which model the subagent should use, as the upstream model id. Must be given together with provider — a model is always referenced by the pair. Omit both to use the Project default model.",
+          },
+          provider: {
+            type: "string",
+            description:
+              "The provider group that model_id belongs to (see the Environment section's Provider). Required whenever model_id is given.",
           },
           yield_time_ms: {
             type: "number",