feat: add 6 gap-closing skills — browser QA, design system, product lens, canary watch, benchmark, safety guard

Closes competitive gaps with gstack:
- browser-qa: automated visual testing via browser MCP
- design-system: generate, audit, and detect AI slop in UI
- product-lens: product diagnostic, founder review, feature prioritization
- canary-watch: post-deploy monitoring with alert thresholds
- benchmark: performance baseline and regression detection
- safety-guard: prevent destructive operations in autonomous sessions

skills/safety-guard/SKILL.md

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+# Safety Guard — Prevent Destructive Operations
+
+## When to Use
+
+- When working on production systems
+- When agents are running autonomously (full-auto mode)
+- When you want to restrict edits to a specific directory
+- During sensitive operations (migrations, deploys, data changes)
+
+## How It Works
+
+Three modes of protection:
+
+### Mode 1: Careful Mode
+
+Intercepts destructive commands before execution and warns:
+
+```
+Watched patterns:
+- rm -rf (especially /, ~, or project root)
+- git push --force
+- git reset --hard
+- git checkout . (discard all changes)
+- DROP TABLE / DROP DATABASE
+- docker system prune
+- kubectl delete
+- chmod 777
+- sudo rm
+- npm publish (accidental publishes)
+- Any command with --no-verify
+```
+
+When detected: shows what the command does, asks for confirmation, suggests safer alternative.
+
+### Mode 2: Freeze Mode
+
+Locks file edits to a specific directory tree:
+
+```
+/safety-guard freeze src/components/
+```
+
+Any Write/Edit outside `src/components/` is blocked with an explanation. Useful when you want an agent to focus on one area without touching unrelated code.
+
+### Mode 3: Guard Mode (Careful + Freeze combined)
+
+Both protections active. Maximum safety for autonomous agents.
+
+```
+/safety-guard guard --dir src/api/ --allow-read-all
+```
+
+Agents can read anything but only write to `src/api/`. Destructive commands are blocked everywhere.
+
+### Unlock
+
+```
+/safety-guard off
+```
+
+## Implementation
+
+Uses PreToolUse hooks to intercept Bash, Write, Edit, and MultiEdit tool calls. Checks the command/path against the active rules before allowing execution.
+
+## Integration
+
+- Enable by default for `codex -a never` sessions
+- Pair with observability risk scoring in ECC 2.0
+- Logs all blocked actions to `~/.claude/safety-guard.log`