security: harden defaults for network-exposed deployments

[phjlljp]

Summary

Addresses a chain of vulnerabilities that combine into unauthenticated root RCE when repowise is deployed via Docker with default settings (the "Skeleton Key" kill chain: no auth → unrestricted local_path → command injection → root container).

This was identified through a comprehensive security audit with multi-model adversarial validation.

Changes

• deps.py — Fail-closed authentication when REPOWISE_HOST=0.0.0.0 and no API key is set (returns 503). Uses hmac.compare_digest() for constant-time key comparison. Logs a startup warning when network-exposed without auth. Localhost deployments remain open (no UX change).
• schemas.py — Pydantic field_validator on RepoCreate.local_path: rejects .. path segments, requires directory to exist and contain .git. Returns resolved absolute path.
• tool_why.py — Sanitizes stem to [a-zA-Z0-9_\-.] before passing to git log --grep. Adds -- separator to prevent argument injection.
• Dockerfile — Runs as non-root repowise user. Copies Node.js from the builder stage instead of piping curl | bash (eliminates supply chain risk).
• docker-compose.yml — Binds ports to 127.0.0.1 (loopback only). Requires REPOWISE_API_KEY and REPO_PATH env vars (docker-compose fails fast if unset). Mounts repos read-only.

Security Model

The fix adopts a dual-mode security model:

• Local CLI (repowise serve): binds 127.0.0.1, no auth required — unchanged developer experience
• Docker/network: binds 0.0.0.0, requires API key, non-root container, read-only repo mount

Kill Chains Addressed

Chain	Findings	Status
Unauthenticated root RCE	No auth + path traversal + cmd injection + root Docker	Blocked (4 independent mitigations)
Credential theft via browser	CORS + plaintext keys	Partially mitigated (auth required for network)
Webhook abuse	No webhook auth	Not addressed (separate PR)

Test plan

• repowise serve on localhost still works without API key
• Docker build succeeds and container runs as non-root (docker exec <id> whoami → repowise)
• docker-compose up fails if REPOWISE_API_KEY or REPO_PATH not set
• POST /api/repos with local_path=/etc returns 422 validation error
• POST /api/repos with local_path=/tmp/valid-repo (with .git) succeeds
• API returns 503 when REPOWISE_HOST=0.0.0.0 and no key set
• API returns 401 on bad key, 200 on correct key with REPOWISE_API_KEY set

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