feat: add HTTP bearer authentication

[shivros]

Summary

• protect every HTTP endpoint except GET /health with optional static IRIS_API_TOKEN bearer authentication
• reject public/wildcard binds when no token is configured, while permitting deployment-agnostic private address classes
• document authenticated self-hosting and the unauthenticated safety boundary

Verification

• cargo build --all-targets
• cargo test --all-targets
• cargo clippy --all-targets -- -D warnings
• cargo fmt --all -- --check
• cargo run -p iris-codegen --bin iris-codegen -- check

Agent acceptance

curl -H "Authorization: Bearer ${IRIS_API_TOKEN}" http://127.0.0.1:9876/providers

[shivros]

🤖 Automated Review Panel

Reviewer A — gpt-5.6-terra

APPROVE. No release-blocking issues: middleware covers all registered routes except exact /health; malformed/missing/wrong bearer values return 401; fixed-size SHA-256 digest comparison avoids early exit. No-token binding is restricted to numeric loopback/private/CGNAT/ULA ranges with a warning.

Reviewer B — Gemini 3 Flash

APPROVE. Confirmed global route coverage, 401 behavior, token comparison, and deployment-agnostic non-public binding policy. No Tailscale-specific behavior introduced.

[shivros]

Auto-Merge Gate

Verdict: MERGE (squash) — confidence 0.90

Rationale: PR implements COD-429 exactly: optional static IRIS_API_TOKEN bearer auth via Axum middleware covering every route except exact /health (missing/malformed/wrong → 401), constant-time SHA-256 digest comparison, blank-token hardening, and refusal of public/wildcard binds (loopback/RFC1918/CGNAT/ULA allowed) with a loud startup warning when unset. README documents the threat model. Both review-panel reviewers (GPT-5.6 Terra, Gemini 3 Flash) APPROVE with no unresolved findings.

Checks observed (all green): Test, Format Check, Clippy, Secret Scan, Dependency Audit, Creed context drift.

Independent local verification (disposable clone, TechGodHQ/iris @ 759bda9): cargo build --all-targets ✓ · cargo test --all-targets ✓ (all suites ok) · cargo clippy --all-targets -- -D warnings ✓ · cargo fmt --all -- --check ✓.

Scope limits: Auth feature addition per linked ticket; no secrets exposed, rotated, or deleted; no production cutover in this merge (published images follow release tags). Linked Linear COD-429 scanned for manual-review markers — none.