docs: define greppability conventions for new seams

[remember993]

Summary

Adds repository-wide greppability conventions for future protocol seams, with concrete rollout-engine and weight-sync examples.

What changed

• Defines capability-stem naming patterns for protocols, configs, contexts, and registry specs.
• Requires descriptive resolver names and a searchable user-key -> registration -> spec/adapter -> resolver -> consumer path.
• Documents the existing algorithm and model-adapter registries as authoritative, without renaming APIs or changing runtime behavior.

Closes #57

Validation

• git diff --check
• Strict Sphinx HTML build with sphinx-build -E -a -W --keep-going -b html docs <temp-dir> using the documented Shibuya theme
• No GPU, model download, or runtime tests required; documentation-only change