docs: align reference pages and experiments with the runtime

[imran-siddique]

The deeper cA2A references still described Cedar, sealed transport, and TRACE binding as unimplemented. The inbound flow also put sealing on the callee and described authorization records as proof of completed work. This updates 14 pages to the implemented checks, distinguishes caller and callee appraisal, and explains the limits of unsigned provenance.

Three documented experiments failed before reaching their intended checks because they omitted trusted roots. They now retain their generated authority separately and pass it explicitly. The tutorials run in sequence, distinguish signature tampering from correctly signed scope escalation, and demonstrate a fully rewritten unsigned path that still passes consistency checks. CI executes all six experiment entry points and the exact tutorial blocks.

Validation: 567 unit/conformance tests passed, 6 skipped (90.11% coverage); Ruff lint/format and mypy passed. MkDocs build passed with the existing missing-SPONSORS navigation warning addressed by #153. Browser checked the architecture reference at desktop and 390px width. No new hardware run was performed; C6 uses synthetic evidence.

This supplements #153 without changing its landing-page/quickstart files. Maintainer review requested before merge.

[imran-siddique]

@agentrust-io/maintainers please review and approve this documentation follow-up. It corrects the call sequence and trust boundaries, and makes the documented experiments runnable. All CI checks are green; local validation passed 567 tests with 6 skips.