feat(detector): add PatchWarden detection

[jiezeng2004-design]

Summary

• detect PatchWarden as an OpenSource AI CLI when the patchwarden binary is on PATH
• resolve npm version and install metadata without executing the MCP stdio entrypoint
• avoid treating stale .patchwarden/ task artifacts as installation evidence
• document the detector and its metadata-only version behavior

Why

PatchWarden is installed as an npm CLI, but its executable starts an MCP stdio
server rather than behaving like a conventional --version command. Detector
version probing must therefore use static package metadata and return unknown
when metadata is unavailable.

The detector is deliberately binary-first. A repository can retain a
.patchwarden/ directory after the CLI has been removed, so project artifacts
alone are not reliable installation evidence.

Validation

• gofmt -d internal/detector/aicli.go internal/detector/aicli_test.go
• go test ./internal/detector -run PatchWarden -count=1
• go vet ./...
• cross-platform go build ./... for Windows, Linux, and macOS amd64 with CGO_ENABLED=0
• go mod tidy leaves go.mod and go.sum unchanged
• git diff --check

The four focused tests cover Unix npm metadata, Windows npm shims, missing
metadata without process execution, and stale project artifacts.

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