Keep the personal half of the desktop in one place, and ask before installing it

Agent instructions, skills, SSH host aliases and expansion triggers are worth
having identical on every machine one person owns, and belong in none of the
shared configuration. They live in user/ now, with a manifest saying where each
piece goes and a link-user stage that puts it there.

That stage does nothing unless the machine said yes. Somebody who clones Panama
to try the desktop keeps their own ~/.claude/CLAUDE.md exactly where it was;
the question names the destinations and defaults to no. Anything displaced goes
to config/old rather than being deleted.

~/.claude/CLAUDE.md and ~/.codex/AGENTS.md were byte-identical copies of one
file, which is the drift this exists to prevent.

Also adds the vitals toggles for the battery and Claude usage readouts, which
had preferences and no way to reach them.

user/agents/skills/slidev/references/core-syntax.md

@@ -0,0 +1,155 @@
+---
+name: syntax
+description: Core Markdown syntax for Slidev presentations
+---
+
+# Slidev Markdown Syntax
+
+Core Markdown syntax for Slidev presentations.
+
+## Slide Separator
+
+Use `---` with blank lines before and after:
+
+```md
+# Slide 1
+
+Content
+
+---
+
+# Slide 2
+
+More content
+```
+
+## Headmatter (Deck Config)
+
+First frontmatter block configures the entire deck:
+
+```md
+---
+theme: default
+title: My Presentation
+lineNumbers: true
+---
+
+# First Slide
+```
+
+## Per-Slide Frontmatter
+
+Each slide can have its own frontmatter:
+
+```md
+---
+layout: center
+background: /image.jpg
+class: text-white
+---
+
+# Centered Slide
+```
+
+## Presenter Notes
+
+HTML comments at end of slide become presenter notes:
+
+```md
+# My Slide
+
+Content here
+
+<!--
+These are presenter notes.
+- Remember to mention X
+- Demo the feature
+-->
+```
+
+## Code Blocks
+
+Standard Markdown with Shiki highlighting:
+
+````md
+```ts
+const hello = 'world'
+```
+````
+
+With features:
+````md
+```ts {2,3}              // Line highlighting
+```ts {1|2-3|all}        // Click-based highlighting
+```ts {monaco}           // Monaco editor
+```ts {monaco-run}       // Runnable code
+```ts twoslash           // TypeScript types
+```
+````
+
+## LaTeX Math
+
+Inline: `$E = mc^2$`
+
+Block:
+```md
+$$
+\frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
+$$
+```
+
+## Diagrams
+
+Mermaid:
+````md
+```mermaid
+graph LR
+  A --> B --> C
+```
+````
+
+PlantUML:
+````md
+```plantuml
+@startuml
+Alice -> Bob : Hello
+@enduml
+```
+````
+
+## Comark Syntax
+
+Enable with `comark: true`:
+
+```md
+[styled text]{style="color:red"}
+![](/image.png){width=500px}
+::component{prop="value"}
+```
+
+## Scoped CSS
+
+Styles apply only to current slide:
+
+```md
+# Red Title
+
+<style>
+h1 { color: red; }
+</style>
+```
+
+## Import Slides
+
+```md
+---
+src: ./pages/intro.md
+---
+```
+
+Import specific slides:
+```md
+---
+src: ./other.md#2,5-7
+---
+```