Quality-improve 10 v7.0.0-era engineering skills

Applies three consistent fixes across the v7.0.0 batch:
- Rename `## Output Structure` → `## Output Format` for consistency
- Wrap output template in `---` document separators (code-review-checklist,
  debugging-log-analyser needed full structural upgrade; remaining 8 already
  had the wrapper)
- Remove `## Example Trigger Phrases` section from all 10 skills

Skills updated: code-review-checklist, debugging-log-analyser,
changelog-generator, pr-description-writer, system-design-interview,
test-strategy-doc, runbook-writer, incident-postmortem, api-docs-writer,
architecture-decision-record

Both `skills/` and `plugins/pm-engineering/skills/` copies synced.

https://claude.ai/code/session_01C3HwChrccJd145vJ6Z7ajF

plugins/pm-engineering/skills/incident-postmortem/SKILL.md

@@ -21,7 +21,7 @@ Ask the user for these if not provided:
 - **Initial thoughts on root cause**
 - **Action items already identified** (optional)
 
-## Output Structure
+## Output Format
 
 ---
 
@@ -135,10 +135,3 @@ Rules for action items:
 - [ ] Every action item has an owner and due date
 - [ ] "What went well" section is genuine, not token
 - [ ] Executive summary is readable by non-technical leadership
-
-## Example Trigger Phrases
-
-- "Write a postmortem for the [incident name] outage"
-- "Help me write a P1 incident report"
-- "Generate an RCA document for [service] going down on [date]"
-- "Draft a blameless postmortem from these notes: [paste notes]"