docs: standardize Ankhorage project structure

[artiphishle]

Summary

• replace the canonical ankhorage-project-structure skill with the approved repository-wide structure contract
• explicitly exclude ankhorage/contracts before any structural rule applies
• make required-skill resolution portable through <repo-root>/.agents/skills/... rather than paths relative to the project-structure skill installation
• standardize product capabilities under src/features/
• standardize repository and feature constants under topic-scoped constants/<topic>.ts
• include Surface and ZORA in the migration order
• restore the managed hexagonal-architecture SKILL.md files to the unmodified ECC v2.2.0 source so dependency direction is one-way: project-structure may load Hexagonal Architecture, but Hexagonal Architecture does not refer back to project-structure
• update the managed-skill contract tests to enforce the new portable contract instead of obsolete wording
• add the required patch changeset

This establishes the canonical structure required by the BottomSheet work in ankhorage/zora#400.

Closes #198
Related: ankhorage/zora#400