fix(psp-1): rewrite Section 6 and restructure Sections 10 - 11

- Rewrote Section 6 (Semantic Pinning) for clarity and separation of
  pinning, snapshot formats, delegation compatibility, and fail-closed rules.
- Clarified channel binding profiles as PSP-3/PSP-4 labels only.
- Renumbered and reorganized Section 10 (Presentations) to RFC-style layout:
  normative vs informative subsections, merged structure/projection content.
- Marked `schemesSnapshotId` as REQUIRED; `channelLatticeId` optional unless
  `channelGeq` used.
- Added stable MDX anchors (e.g. #security-considerations) and updated
  cross-references to avoid hard-coded section numbers.
- Removed normative recursion on PSP-2; receipts now conditional on support.
- Fixed duplicate numbering and minor typos in Sections 10-11.

Author: CMCDragonkai