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 |

content/posts/writing-template.md

@@ -17,15 +17,15 @@ description: 一篇文章演示全站可用的排版能力：标题层级、彩
 
 段落之间空一行即可。行内可以**加粗**、*斜体*、~~删除线~~、`行内代码`，也可以放[普通链接](https://astro.build)。
 
-## 二、彩色强调：一页不超过三处
+## 二、彩色强调：想用多少用多少
 
-纪律来自设计基线：站点外壳是灰阶的，颜色只用来给正文某一个判断加重，一页最多三处。超过就变成花哨。
+颜色现在**没有次数限制**（2026-11-02 起取消了原来的「一页最多三处」）。唯一还守着的是外壳：导航、页脚、按钮、背景保持灰阶——外壳是气质，正文是表达。
 
 <span class="c-blue">第一处：一个关键结论用蓝色提出。</span> 后面照常叙述。
 
 <span class="c-red">第二处：需要警示的坑用红色。</span> 比如「改完 Markdown 插件必须清 `node_modules/.astro`，否则改动静默不生效」。
 
-<span class="c-green">第三处：确认可行的路径用绿色。</span> 三处之后，本节不再上色。
+<span class="c-green">确认可行的路径用绿色。</span> 想让整段都是重点也不必克制，把它们都标出来即可。
 
 可用色相共 8 组（blue / teal / green / yellow / orange / red / pink / purple），每组有标准与 `-soft` 两档；另有 4 个灰阶层级类（`ink-muted` / `ink-warm` / `ink-cool` / `ink-faint`）用于降调，不算彩色额度。
 
@@ -83,7 +83,7 @@ export function sortPosts<T extends Post>(posts: T[]): T[] {
 
 | 能力 | 写法 | 注意 |
 | --- | --- | --- |
-| 彩色强调 | `<span class="c-blue">` | 一页 ≤3 处 |
+| 彩色强调 | `<span class="c-blue">` | 不限次数（外壳仍灰阶） |
 | 换字族 | `<span class="font-kai">` | 整页换会拉字体体积 |
 | 图片 | `![说明](./assets/<slug>/x.jpg)` | 体积纪律见写作指南 |
 | 视频 | frontmatter `video:` | 放 public/media，≤50MB |