Extract prime.go into focused files:
- prime_session.go: session ID handling, hooks, persistence
- prime_output.go: all output/rendering functions
- prime_molecule.go: molecule workflow context
- prime_state.go: handoff markers, session state detection
Main prime.go now ~730 lines with core flow visible as "table of contents".
No behavior changes - pure file organization following Go idioms.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
