feat: add browse access to /debug for visual verification

Debug skill can now use the browse binary to visually reproduce bugs,
take screenshots as evidence, and verify fixes. This makes /debug
effective for web app bugs when spawned as a sub-agent from /qa.

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

debug/SKILL.md.tmpl

@@ -16,6 +16,8 @@ allowed-tools:
 
 {{PREAMBLE}}
 
+{{BROWSE_SETUP}}
+
 # Systematic Debugging
 
 ## Iron Law
@@ -42,6 +44,14 @@ Gather context before forming any hypothesis.
 
 4. **Reproduce:** Can you trigger the bug deterministically? If not, gather more evidence before proceeding.
 
+5. **Visual reproduction (if browser-testable bug):** Use the browse binary to reproduce the bug:
+   ```bash
+   $B goto <affected-url>
+   $B screenshot screenshots/debug-ISSUE-NNN-repro.png
+   $B console --errors
+   ```
+   Compare what you see against the reported symptom. If the bug is not reproducible visually, that's useful evidence too — the root cause may be in data flow, not rendering.
+
 Output: **"Root cause hypothesis: ..."** — a specific, testable claim about what is wrong and why.
 
 ---
@@ -120,6 +130,14 @@ Once root cause is confirmed:
 
 Run the test suite and paste the output.
 
+**Visual verification (if browser-testable bug):**
+```bash
+$B goto <affected-url>
+$B screenshot screenshots/debug-ISSUE-NNN-fixed.png
+$B console --errors
+```
+Compare against the original reproduction screenshot. The bug should no longer be present.
+
 Output a structured debug report:
 ```
 DEBUG REPORT