DX: create first-contributor fast paths #682

Problem

The project is effectively single-author plus bot/test identities, and the docs style amplifies bus-factor risk. A new external contributor needs narrow, non-philosophical entry paths.

Evidence at e948217274fe:

• git shortlog -sn HEAD shows contributions are dominated by James Ross / J. Kirby Ross plus test and bot identities.
• Current docs are extensive but require significant project vocabulary before many tasks become obvious.

Mitigation Plan

• Add CONTRIBUTING fast paths: docs-only PR, fixture-only PR, emitter test PR, CLI bug PR.
• Create small good-first issues tied to one file and one test command.
• Add maintainer-independent release and triage runbooks with exact commands.
• Mark advanced/system-theory docs as design background, not required reading.
• Add public examples from at least one sibling consumer while keeping ownership boundaries explicit.

Acceptance Criteria

• A first-time contributor can identify a safe issue, branch, test command, and PR checklist in under 10 minutes.
• Good-first issues avoid internal vocabulary unless the issue is specifically about docs vocabulary.
• Contributor docs distinguish required workflow from optional architecture background.