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/web/src/lib/format.ts

@@ -31,6 +31,17 @@ export function humanizeDuration(ms: number): string {
   return `${m}m${Math.round(s % 60)}s`;
 }
 
+/**
+ * Duration format for a still-running timer: whole seconds only (`0s`, `7s`, `1m3s`),
+ * counting up (floor, never showing a second early). Decimals are reserved for settled
+ * durations (humanizeDuration above) — a live timer showing tenths reads as jitter.
+ */
+export function humanizeDurationLive(ms: number): string {
+  const s = Math.max(0, Math.floor(ms / 1000));
+  if (s < 60) return `${s}s`;
+  return `${Math.floor(s / 60)}m${s % 60}s`;
+}
+
 /** Add an explicit sign to a delta string: non-negative gets `+`, negative already has `-` (negative when context shrinks after compaction). */
 export function signedDelta(formatted: string): string {
   return formatted.startsWith("-") ? formatted : `+${formatted}`;