feat(pr): add pr skill for writing PR bodies

Adds a user-invoked pr skill with a Summary/Evidence/Merge Danger
template, visual-format guidance adapted from Dex Horthy's show-me
skill (attribution in CREDITS.md), and an openai agent interface.

skills/engineering/pr/CREDITS.md

@@ -0,0 +1,3 @@
+# Credits
+
+The **Summary** section's menu of visuals (pseudocode, call trees, component trees, file trees, Mermaid, diffs) and its placement guidance come from [Dex Horthy](https://github.com/dexhorthy)'s [`show-me`](https://github.com/humanlayer/humanlayer) skill, reproduced almost word for word and aimed at a diff instead of a live conversation. `pr` does not depend on `show-me` as a skill (it isn't part of this repo, and a hard dependency would break standalone installs), so the content is copied in rather than pointed at; this file is the attribution a dependency would otherwise have carried.

skills/engineering/pr/SKILL.md

@@ -0,0 +1,170 @@
+---
+name: pr
+description: "Use when writing a PR body."
+metadata:
+  credits:
+    skill: show-me
+    author: Dex Horthy
+    organisation: Humanlayer
+    url: "https://github.com/humanlayer/skills/blob/main/plugins/show-me/skills/show-me/SKILL.md"
+---
+
+Use this template for writing the PR body:
+
+```markdown
+## Summary
+
+<diagram, diff-sketch, or tree>
+
+## Evidence
+
+- **Before:** <screenshot/output/failing test run>
+  **After:** <screenshot/output/passing test run>
+
+## Merge Danger
+
+**Door:** <one-way or two-way>
+
+<optional: description>
+
+**Blast Radius:** <one-word description>
+
+<optional: potential ramifications of merge>
+```
+
+## Sections
+
+Skip all preambles and keep prose brief. Use the user's domain language from `GLOSSARY.md`.
+
+### Summary
+
+Pick the smallest view that makes the key point clear.
+
+- Show logic or an algorithm as pseudocode:
+
+```text
+on(save)
+  if content is unchanged
+    return cached result
+  write new content
+  return fresh result
+```
+
+- Show runtime control flow as a call tree:
+
+```text
+submitForm
+  createSession
+    persistPrompt
+    launchAgent
+  navigateToSession
+```
+
+- Show UI structure as a component tree, including state and module boundaries that matter:
+
+```text
+<SessionPage> (apps/example/src/routes/session.tsx)
+  useSessionEvents()
+  <SessionToolbar>
+    <RunSkillButton> (packages/ui)
+```
+
+- Show file responsibility or a broad refactor as a shallow file tree:
+
+```text
+src/
+├── commands/       # parses user actions
+├── sessions/       # owns session state
+└── transport/      # sends API requests
+```
+
+- Show component interaction, control flow, or data flow with Mermaid:
+
+```mermaid
+sequenceDiagram
+    participant User
+    participant UI
+    participant Daemon
+    User->>UI: choose command
+    UI->>Daemon: send expanded prompt
+    Daemon-->>UI: stream result
+```
+
+- Use `diff` when the point is what changes and the surrounding shape already exists. Match the diff shape to the topic.
+
+For a component change:
+
+```diff
+ <SessionPage>
+   useSessionEvents()
+   <SessionToolbar>
++    <RunSkillButton />
+   <SessionTimeline>
++    <SkillResultCard />
+```
+
+For a file-layout change:
+
+```diff
+ src/
+ ├── commands/
++│   └── show-me.ts       # expands the slash command
+ ├── sessions/
+-└── transport.ts
++└── transport/
++    ├── client.ts
++    └── stream.ts
+```
+
+For a call-tree or call-stack change:
+
+```diff
+ submitForm
+   createSession
+     persistPrompt
++    expandSkillMention
+     launchAgent
+-  navigateToSession
++  navigateToSession
++    subscribeToEvents
+```
+
+For a state or control-flow change:
+
+```diff
+ on(save)
+-  write content
++  if content is unchanged
++    return cached result
++  write new content
++  invalidate cache
+```
+
+- Show the whole block when most of it is new, when omitted context would hide ownership or order, or when the user needs a copyable target shape:
+
+```ts
+function expandSkill(command: string): string {
+  const skillName = command.slice(1);
+  return `use the ${skillName} skill`;
+}
+```
+
+#### Guidance
+
+Place each visual next to the short text it supports. Keep only the calls, files, props, states, and boundaries needed to answer the user's current question or the options to resolve the current discussion point.
+
+You may use one of these, you may use several, it is unlikely you will use all of them. Use your judgement and don't overwhelm the user.
+
+### Evidence
+
+Concrete evidence that the change works. Show a before and after.
+
+Screenshots are S-tier - when the environment is set up for it and the change is visual.
+
+Execution-based evidence is A-tier. Test results, console output. Show the exact test that now fails and passes, using pseudocode.
+
+### Merge Danger
+
+Describe whether it's a one-way or two-way door. You can walk back through two-way doors, but not one-way doors. A PR that is cheap to roll back is lower risk. Changes that involve destructive actions or hard-to-reverse decisions are one-way doors.
+
+The blast radius is the potential impact or scope of the changes introduced by this PR. Consider all possibilities. Examples are layout shift, breakages for consumers, mobile responsiveness, etc.

skills/engineering/pr/agents/openai.yaml

@@ -0,0 +1,3 @@
+interface:
+  display_name: "PR"
+  short_description: "Write a PR body that's fast to review"