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/interfaces.zh.md

@@ -89,7 +89,7 @@ interface GenerativeModelConfig {
 `GenerativeModel`(`packages/core/src/llm/generative-model.ts`)把契约落到模型网关 `@prismshadow/agenthub` 的 `AutoLLMClient` 上：
 
 - 网关**有状态**地维护会话历史，每轮只接收新消息；恢复 Session 时经一次性的 `setHistory` 重放已提交历史；
-- 内部的 `EventTranslator` 把网关流式事件翻译为 `partial_*` 分片 + 完整消息，保留 `signature` / `phase` 保真字段，完整消息按 thinking → text → tool_call 顺序落盘；
+- 内部的 `EventTranslator` 把网关流式事件翻译为 `partial_*` 分片 + 完整消息，逐条原样保留不透明的 `fidelity` 保真负载；分段与网关自身的聚合一致——thinking 块由其 fidelity 负载闭合，连续相同的 fidelity 归为同一块(OpenAI 兼容客户端给每条增量盖同一个 `{ reasoning_field }`，不能因此切块)，text 段遇到不同的 `fidelity.phase` 即切分、遇到 `fidelity.signature` 即闭合，合并时 fidelity 键累积；完整消息按 thinking → text → tool_call 顺序落盘；
 - `ToolCallIdAllocator` 处理个别 Provider 用函数名充当调用 id 的情况(入站追加 `#n`、出站剥离)，作用域覆盖整个 Session;
 - Provider 协议差异(工具调用格式、思考内容、流式事件)全部在网关内抹平，见[模型与 Provider](/models)。
 
@@ -169,7 +169,7 @@ interface ToolDefinitionConfig {
 Human 刻意不设计为接口类。SDK 的调用方就是 Human:
 
 ```ts
-const session = await agent.createSession({ workspaceDir, modelId });
+const session = await agent.createSession({ workspaceDir, provider, modelId });
 
 session.run(
   newMessages: OmniMessage[],                    // 输入:Prompt