feat: harden local privacy defaults

[jb-thery]

Summary

• add local-only Ollama network policy by default
• redact common sensitive identifiers before indexing
• add metadata-only access logs and security-audit reporting
• add destroy-index command for generated vector storage removal
• harden MCP with bounded retrieval and security audit tool
• generate release verification artifacts: npm tarball, SHA256SUMS, CycloneDX SBOM, manifest
• document threat model, air-gapped operation, zero telemetry, MCP hardening, RBAC limits, and secure deletion limits
• bump package to 0.3.0

Validation

• pnpm validate
• shasum -a 256 -c SHA256SUMS in release-artifacts/
• node dist/cli.js security-audit --json
• node dist/cli.js destroy-index refuses deletion without --yes