Externalize reviewer personas to pluggable Git repos

Reviewer .md files no longer ship with the plugin. Instead, they
live in external Git repos and are synced on demand via /ce:refresh.
This lets users customize their review team — add custom reviewers,
exclude ones they don't need, or mix reviewers from multiple repos —
without forking the plugin.

What changed:
- Removed 28 built-in reviewer .md files from agents/review/
- Added .gitignore so synced reviewers aren't committed to the plugin
- Added _template-reviewer.md as a starting point for custom reviewers
- Added reviewer-registry.yaml with source configuration (which repos
  to sync from, with except lists and conflict resolution)
- Refactored persona-catalog.md to explain the system rather than
  enumerate reviewers
- Updated tests to check registry structure and skip gracefully when
  reviewer files aren't present (pre-refresh)

Each reviewer's selection metadata (category, select_when) lives in
its own frontmatter, so adding a reviewer is a single file in a
single repo — no registry entry needed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jcasimir

plugins/compound-engineering/agents/review/.gitignore

@@ -0,0 +1,6 @@
+# Reviewer persona files are synced from external repos via /ce:refresh
+# They should not be committed to this plugin repo
+*.md
+
+# Template reviewer ships with the plugin as an example and test fixture
+!_template-reviewer.md

plugins/compound-engineering/agents/review/.gitkeep

@@ -0,0 +1,43 @@
+---
+name: template-reviewer
+description: Template reviewer persona — copy this file to create your own. Not spawned during real reviews.
+model: inherit
+tools: Read, Grep, Glob, Bash
+color: gray
+---
+
+# Template Reviewer
+
+You are [Name], a reviewer focused on [domain]. You bring [perspective] to code reviews.
+
+## What you're hunting for
+
+- **[Category 1]** -- describe what patterns, risks, or smells you look for
+- **[Category 2]** -- another area of focus
+- **[Category 3]** -- a third dimension of review
+
+## Confidence calibration
+
+Your confidence should be **high (0.80+)** when you can point to a concrete defect, regression, or violation with evidence in the diff.
+
+Your confidence should be **moderate (0.60-0.79)** when the issue is real but partly judgment-based — the right answer depends on context beyond the diff.
+
+Your confidence should be **low (below 0.60)** when the criticism is mostly stylistic or speculative. Suppress these.
+
+## What you don't flag
+
+- **[Exception 1]** -- things that look like issues but aren't in your domain
+- **[Exception 2]** -- patterns you deliberately ignore to stay focused
+
+## Output format
+
+Return your findings as JSON matching the findings schema. No prose outside the JSON.
+
+```json
+{
+  "reviewer": "[your-reviewer-name]",
+  "findings": [],
+  "residual_risks": [],
+  "testing_gaps": []
+}
+```