feat: 内置技能全量收录 presentation-forge (#83)

## 概述
将 PPT 工作流技能 **presentation-forge**（原 codex-ppt-skill）以 **builtin
内置技能**形态全量收录进 DesireCore 官方市场。

> 注：本 PR 最初以 entry.json pointer 形态提交，现按仓库负责人意见改为 builtin 层全量
vendoring。分支保留两个提交（pointer → builtin 转换）。

## 形态：builtin 全量 vendoring（遵循 guizang-ppt 先例）
- 全量内容进 `skills/presentation-forge/`：`SKILL.md` + `SKILL.zh-CN.md` +
`references/` + `scripts/` + `styles/`（9 套风格）+ `templates/` +
`schemas/`。
- builtin frontmatter：`version/type/risk_level/status/tags` +
`metadata.i18n`（zh-CN/en-US）+
`market.icon/category/maintainer`，`category: creative`。
- 列入 `builtin-skills.json`（33 项）。
- 附 `LICENSE`（MIT）+ `NOTICE.md` +
`_desirecore/{frontmatter.yaml,upstream.json}` 溯源。
- 溯源 commit：`mashagua/presentation-forge@b7b1a9c`（MIT）。
- 排除非运行内容：`tests/` 夹具、未被任何 vendored 文件引用的 1.3MB 流程图、Codex `agents/` 绑定。

## 变更
- 新增 `skills/presentation-forge/`（全量内容，约 440KB）
- `builtin-skills.json`：新增 `presentation-forge`（32 → 33）
- `manifest.json`：`stats.totalSkills` 60 → 61，`version` 1.2.26 →
1.2.27，`lastUpdated` → 2026-08-10
- `README.md`：built-in 32 → 33、external 29 → 28、total 61 不变，两处代码块同步

## 验证
```
uv run scripts/i18n/validate-i18n.py
OK: no i18n issues found.
```
stats 公式核对：entry.json 目录 28 + SKILL.md 目录 33 = 61 = manifest.totalSkills
✓

---------

Co-authored-by: Yige <a@wyr.me>
Co-authored-by: yige <yige@yigedeMacBook-Neo.local>

skills/presentation-forge/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Ronnie2025
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.