Canonicalize pattern reference syntax and documentation

[irl-dan]

Problem

OpenProse pattern references are conceptually supported but documented inconsistently. The relationship among use, pattern:, with:, and config: lacks one canonical, cross-linked definition. ### Patterns appears in repository examples/tests but is absent from the canonical Contract Markdown section table, and some documentation references a nonexistent Forme pattern-expansion section.

This makes it difficult for Compose and authors to distinguish importing a pattern, instantiating it, binding its slots, and configuring it.

Desired property

One self-evident authoring path explains how a Contract references and instantiates local and external patterns, how dependency installation and aliases apply, how slots/config are validated, and how Forme expands the instance. Examples and canonical section tables agree.

Smallest plausible change

• Choose and document the canonical placement for pattern instances.
• Define use, pattern:, with:, and config: together with one complete example.
• Decide whether ### Patterns is canonical; add it to Contract Markdown or remove/migrate its uses.
• Repair broken Forme cross-references.
• Add a conformance test guarding the chosen form.

Alternatives

• Introduce new pattern-import syntax.
• Keep pattern instances as free-form YAML and document only conventions.

No new syntax is recommended until the existing surface is made internally consistent.