feat(groove): add IPv6T spec and Graduated Trust paper

spec/IPV6T.adoc — Typed Payload Framing for IPv6:
  - 105-byte GRV6 frame header (magic, version, flags, type_hash,
    cap_hash, prov_hash, payload_length)
  - Lives inside TCP payload — passes through every middlebox
  - Trust level encoding via flags (TYPED, PROVEN, ATTESTED)
  - Frame detection, type hash generation (comptime + runtime)
  - Receiver behaviour: early rejection, provenance validation
  - Honest Section 4.3: runtime validation still required on WAN
  - Security considerations: TLS, fingerprinting, replay
  - Comparison table vs Protobuf, JSON Schema, gRPC, REST+OpenAPI
  - Testing: 5 tests, <50 lines each, <1 second total

docs/graduated-trust.tex — Third paper in the trilogy:
  "Graduated Trust: A Spectrum of Type Safety from Localhost to
   the Open Internet"
  - Five trust levels: Untyped → Declared → Attested → Verified → Proven
  - Each level has honest costs, guarantees, and limitations
  - Security analysis table: what each level defends against
  - "The Path Upward" — incremental upgrade from L0 to L4
  - Explicit honesty: "IPv6T brings type awareness, not type safety"
  - Targets cs.NI/cs.CR/cs.PL, subsequently NSDI/USENIX Security

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath