fix: align Markdown guidance and live interop reporting

[dasiths]

This PR aligned regular Markdown files with the repository authoring convention
and made the external live interoperability sample distinguish complete draft-10
success from partial compatibility.

Changes

Live interoperability

• Validated Accept-Signature as a structured-field dictionary containing the
  required covered components
• Required exact statuses, valid compact resource-token encoding, and expected
  identity JSON before a live mode could pass
• Treated the external legacy person-token response as an unsupported draft-10
  requirement without contacting the Person Server
• Skipped the impossible three-party exchange and returned exit code 2 when live
  interoperability was incomplete
• Added deterministic tests for malformed headers, token segments, JSON types,
  missing claims, and valid responses
• Added a challenge-handler regression confirming unknown requirements remained
  unsatisfied and did not mutate client state

Markdown authoring

• Added repository instructions that kept YAML frontmatter only in customization
  files that require machine-readable metadata
• Removed frontmatter from regular Markdown files and restored one level-1 title
  where needed
• Regenerated the frozen documentation surface inventory

Related Issues

None.

Validation

• dotnet test AAuth.slnx: 2,906 passed
• Live classifier and unknown-requirement tests: 27 passed
• Challenge-handler tests: 48 passed
• Documentation inventory and link checks: 2 passed
• External live check: Modes 1 and 2a passed; Mode 2b correctly failed on the
  legacy person-token requirement; Mode 3 was skipped; exit code 2
• git diff --check: passed
• Independent PR review: no findings

Notes

whoami.aauth.dev currently returns the pre-draft-10 person-token requirement
for scoped access. The SDK did not add a compatibility fallback. Full external
Person Server authorization will become testable when the resource emits
requirement=auth-token with a valid resource-token parameter.