chore: add CLAUDE.md, /verify skill, and gofmt-on-edit hook

Author: shijiashuai

.claude/settings.json

@@ -0,0 +1,16 @@
+{
+  "hooks": {
+    "PostToolUse": [
+      {
+        "matcher": "Write|Edit",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "jq -r '.tool_input.file_path // .tool_response.filePath' | { read -r f; case \"$f\" in *.go) gofmt -w \"$f\" 2>/dev/null ;; esac; } || true",
+            "timeout": 10
+          }
+        ]
+      }
+    ]
+  }
+}

.claude/skills/verify/SKILL.md

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+---
+name: verify
+description: Run the full CI check suite locally — build, test with race detector, and lint.
+---
+
+Run the full verification suite that CI runs:
+
+1. Build: `go build ./...`
+2. Test: `go test -race -count=1 -coverprofile=coverage.out ./...`
+3. Vet: `go vet ./...`
+4. Lint: `golangci-lint run`
+
+Report pass/fail for each step. If any step fails, show the relevant output and stop.

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project
+
+Go 1.22+ WebSocket signaling server for WebRTC P2P audio/video. Backend: `cmd/server/main.go` + `internal/signal/`. Frontend: vanilla JS in `web/` (no bundler, no framework).
+
+## Commands
+
+- **Build**: `go build ./...`
+- **Test**: `go test -race -count=1 ./...`
+- **Lint**: `golangci-lint run` (config: `.golangci.yml`, 11 linters including staticcheck, revive, gocritic)
+- **Run server**: `go run ./cmd/server` (listens on `:8080`)
+- **Single test**: `go test -race -run TestName ./internal/signal/`
+
+## Code Style
+
+- Go: tabs, `gofmt`. JS/CSS/HTML: 2-space indent (see `.editorconfig`).
+- US English spelling (enforced by misspell linter).
+- No dot imports, no blank imports (enforced by revive).
+
+## Commits
+
+Use [Conventional Commits](https://www.conventionalcommits.org/): `feat:`, `fix:`, `docs:`, `refactor:`, `test:`, `chore:`.
+
+## Environment Variables
+
+| Variable | Default | Purpose |
+|:---------|:--------|:--------|
+| `ADDR` | `:8080` | HTTP listen address |
+| `WS_ALLOWED_ORIGINS` | `localhost` | Comma-separated origins; `*` for all |
+| `RTC_CONFIG_JSON` | public STUN | JSON ICE/TURN config passed to browser |