Phase 3: /qa skill — systematic QA testing with health scores

New /qa skill for systematic web app QA testing. Three modes:
- full: 5-10 documented issues with screenshots and repro steps
- quick: 30-second smoke test with health score
- regression: compare against saved baseline

Includes issue taxonomy (7 categories, 4 severity levels), structured
report template, health score rubric (weighted across 7 categories),
framework detection guidance (Next.js, Rails, WordPress, SPA).

Also adds browse/bin/find-browse (DRY binary discovery using git
rev-parse), .gstack/ to .gitignore, and updated TODO roadmap.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

browse/bin/find-browse

@@ -0,0 +1,11 @@
+#!/bin/bash
+# Find the gstack browse binary. Echoes path and exits 0, or exits 1 if not found.
+ROOT=$(git rev-parse --show-toplevel 2>/dev/null)
+if [ -n "$ROOT" ] && test -x "$ROOT/.claude/skills/gstack/browse/dist/browse"; then
+  echo "$ROOT/.claude/skills/gstack/browse/dist/browse"
+elif test -x "$HOME/.claude/skills/gstack/browse/dist/browse"; then
+  echo "$HOME/.claude/skills/gstack/browse/dist/browse"
+else
+  echo "ERROR: browse binary not found. Run: cd <skill-dir> && ./setup" >&2
+  exit 1
+fi