v2.7.0

pmcp v2.7.0 — Phase 73–79 + RUSTSEC-2026-0098/0099/0104 fix

Highlights:
- Security: resolve three transitive rustls-webpki 0.101.7 advisories
  by switching workspace AWS SDK deps to default-features=false with
  the modern default-https-client TLS path (rustls 0.23 / rustls-webpki
  0.103 via aws-lc-rs).
- pmcp 2.7.0: Phase 75 / 75.5 cognitive-complexity refactors across
  streamable_http_server, schema_utils, path_validation, json_simd,
  workflow::task_prompt_handler, and pmcp-macros. CI PMAT gate at cog
  25 / hard-cap 50.
- cargo-pmcp 0.13.0: Phase 79 widget pre-build orchestrator, post-deploy
  verifier hook with PostDeployReport contract, --format=json on test
  subcommands, --embed-widgets scaffold, doctor widget-rerun.
- pmcp-macros 0.6.1, mcp-preview 0.3.1, pmcp-server 0.2.3,
  pmcp-code-mode 0.5.1 — all patch bumps covering content changes
  since their last publish.
- mcp-tester 0.6.0 (already bumped in-flight from 0.5.3) publishes
  unchanged.

PR #253. CI green on 256d28ca (gate, Quality Gate, PMAT, security_audit
all success).