docs: align dependency resolution with current contract model

[SamCT86]

Summary

• remove retired ### Services, ### Ensures, and system/service dependency terminology from deps.md
• describe dependency discovery around use and pattern: references only
• align Forme/VM dependency wording with current Requires → Maintains and Parameters → Returns contracts
• add a focused regression assertion so retired dependency syntax is not reintroduced

Use Case / Run Evidence

Issue #165 documents stale dependency guidance that can send agents/authors toward syntax the current language has retired. Closes #165.

Design Boundary

Documentation/conformance only. No VM, Forme, CLI, resolver, or runtime behavior changes.

Testing

Freshly synchronized to upstream main@0ab7237ced4ac29ca002c94878e69c5cbf6b1ea6.

• exact PR head: 61880b64625ee77fd330d636cfa7f598b3d1b82b
• focused skill-meta suite: 28/28 pass
• full corepack pnpm test: 305/305 pass across 19 files
• git diff --check: pass
• current PR diff remains exactly skills/open-prose/deps.md plus tests/open-prose/skill-meta/skill-meta.test.ts

GitHub Actions are presently action_required with no jobs started, so maintainer approval is still needed before hosted CI can run.

Residual Risk / Follow-ups

This PR intentionally does not change language semantics; it only removes stale dependency documentation and guards that boundary.