docs(writing): 取消彩色强调次数限制，补灯箱 caption 排版说明

用户原话：「色彩强调不要设置限制，取消一页不超过三处的限制」。原「一页 ≤3 处」
是文档纪律（代码层从未硬性拦截），故改动集中在文档、模板文章与后台提示：

- 写作指南 / 管理台：改为「彩色不限次数」，同时明确仍守的另一条红线是
  **外壳灰阶**（导航/页脚/按钮/背景不染色）——外壳是气质，正文是表达
- 写作模板文章中英双语同步：章节改名「想用多少用多少」，删掉"三处之后不再上色"
  的示范约束，表格里「一页 ≤3 处」改为「不限次数（外壳仍灰阶）」
- 顺带补灯箱 caption 文档：照片说明支持 markdown + 排版类，深底自动取暗档；
  以及灯箱四种关闭路径（右上 ×、Esc、点背景、1× 时点图）

验证: 构建 exit 0；全仓 grep 「≤3 处/页」只剩「已取消」的历史说明

Spec: 2026-11-02_blog-5i-fonts-polish (T5)

Co-authored-by: GLM-5.3

content/posts-en/writing-template.md

@@ -18,15 +18,15 @@ Use `##` for a section and `###` for a subsection. **Never use `#`** — the pos
 
 Leave a blank line between paragraphs. Inline you can use **bold**, *italic*, ~~strikethrough~~, `inline code`, and [ordinary links](https://astro.build).
 
-## 2. Colour emphasis: three per page at most
+## 2. Colour emphasis: as much as you need
 
-The rule comes from the design baseline: the shell is greyscale, so colour exists to weight one judgement in the body — three per page, maximum. More than that and it turns loud.
+Colour is **no longer capped** (the old "three per page" limit was lifted on 2026-11-02). The one rule that remains is the shell: navigation, footer, buttons and background stay greyscale — the shell is temperament, the body is expression.
 
 <span class="c-blue">First use: state one key conclusion in blue.</span> Then carry on normally.
 
 <span class="c-red">Second use: warn about a trap in red.</span> For example, “after changing a Markdown plugin you must clear `node_modules/.astro`, or the change silently does nothing”.
 
-<span class="c-green">Third use: confirm a working path in green.</span> After three, this section stays uncoloured.
+<span class="c-green">Confirm a working path in green.</span> If a whole paragraph deserves emphasis, mark the whole paragraph.
 
 There are eight hues (blue / teal / green / yellow / orange / red / pink / purple), each with a standard and a `-soft` variant, plus four greyscale classes (`ink-muted` / `ink-warm` / `ink-cool` / `ink-faint`) for lowering tone — those do not count against the colour budget.
 
@@ -84,7 +84,7 @@ Refer to variables inline like `posts`.
 
 | Capability | Syntax | Note |
 | --- | --- | --- |
-| Colour emphasis | `<span class="c-blue">` | three per page at most |
+| Colour emphasis | `<span class="c-blue">` | no limit (shell stays greyscale) |
 | Typeface | `<span class="font-kai">` | a whole page adds font weight |
 | Image | `![alt](./assets/<slug>/x.jpg)` | see the writing guide for size rules |
 | Video | frontmatter `video:` | lives in public/media, ≤50MB |