chore: add security policy and normalize license placement

SECURITY.md

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+# Security Policy
+
+## Reporting a Vulnerability
+
+**Please do not open a public GitHub issue for security vulnerabilities.**
+
+Report privately to **security@penguintech.io**. If you would like to encrypt your
+report, ask in your first message and we will arrange a key exchange.
+
+Please include whatever you have:
+
+- A description of the vulnerability and the component it affects
+- Steps to reproduce, or a proof of concept
+- Your assessment of the impact
+- Any suggested mitigation
+- How you would like to be credited, if at all
+
+### What happens next
+
+| Stage | Target |
+|---|---|
+| Acknowledgement of your report | Within 48 hours |
+| Initial assessment and severity triage | Within 5 business days |
+| Fix developed and tested | Severity-dependent; critical issues take priority over roadmap work |
+| Coordinated disclosure | Timed with you — we will not publish before you are ready |
+| Public advisory and credit | On release of the fix, crediting you unless you prefer otherwise |
+
+We will keep you updated as the report moves through these stages. If you do not
+hear back within 48 hours, please follow up — a missed report is a bug in our
+process and we want to know about it.
+
+## Supported Versions
+
+| Version | Supported |
+|---|---|
+| 2.1.x | :white_check_mark: |
+| < 2.1 | :x: |
+
+Security fixes land on the current release line. The previous minor version
+receives fixes for high and critical severity issues; older lines do not.
+
+## Safe Harbour
+
+We will not pursue legal action against researchers who act in good faith:
+access only data that is clearly your own or test data, avoid privacy violations
+and service degradation, do not exfiltrate data beyond what is needed to
+demonstrate the issue, and give us reasonable time to fix things before going
+public. Report promptly and we will treat you as a collaborator, not a threat.
+
+## How Squawk Is Built
+
+Security controls that are configuration are security controls someone forgets
+to turn on. These are defaults in this codebase:
+
+- **Multi-tenant isolation** — the tenant boundary is enforced at the query layer
+  and evaluated before any other authorization check
+- **OIDC scope-based authorization** — permissions resolve to scopes, never role
+  names; roles are pre-bundled scope sets
+- **Short-lived JWTs** — one-hour default expiry, refresh tokens rotate on every
+  use, and a reused refresh token revokes the whole chain
+- **Service identity** — SPIFFE-ready, accepting mTLS/X.509-SVID; every
+  inter-service call carries a short-lived signed JWT regardless of transport
+- **Encryption in transit and at rest** — TLS 1.2+ minimum, at-rest encryption on
+  every store holding sensitive data, backups included
+- **PII tokenization** — a single identity table; everything else references UUIDs
+- **Input and output validation** — inputs validated server-side, responses scoped
+  to an explicit schema so an endpoint cannot silently over-share
+- **Rootless containers** — rootless runtime and non-root process, both layers
+- **Default-deny networking** — deny-by-default network policy, filtered egress,
+  external access scoped to the port the service actually serves
+- **Pinned dependencies** — every dependency pinned to an immutable, verified
+  reference; no floating tags
+- **Automated scanning** — SAST, DAST, dependency audit, container, IaC, and
+  secrets scanning run in pre-commit and pre-push hooks as well as CI
+- **Enforced coverage** — 90% minimum across lines, branches, functions, and
+  statements; builds fail below it, and reported bugs get a regression test
+
+## Compliance
+
+Squawk is **designed to support** organizations working toward SOC 2, ISO
+27001, NIST CSF, HIPAA, PCI DSS, and GDPR obligations — through audit logging,
+access control, encryption, and data handling built to those expectations.
+
+This is a statement about architecture, not a certification claim. We do not
+assert that this project is certified under any of these frameworks. Where a
+formal attestation is required, contact us and we will tell you honestly what
+does and does not exist today.
+
+## Security Updates
+
+Advisories are published as GitHub Security Advisories on this repository and
+noted in release notes. Watch this repository's releases to be notified.