emrg: read projects.yml, iterate auto_evolve projects round-robin in evolution loop

[argszero]

Makes the background evolution thread project-aware: reads projects.yml, iterates over auto_evolve=true projects round-robin (one per tick), with per-project session_id and cwd.

Changes (1 file, +66/-8):

• _get_auto_evolve_projects(): new method reads projects.yml, returns auto_evolve=True entries
• run(): loads projects each tick, picks one round-robin, passes to _run_evolution_cycle()
• _run_evolution_cycle(): accepts optional project dict, derives per-project session_id (emrg-evolution-{name}) and cwd
• _build_evolution_prompt(): accepts optional project dict, derives source_dir from project path

Backward compatible: falls back to emrg self-evolution defaults when no auto_evolve projects exist.

Part of multi-project evolution: builds on #32 (projects.yml), sets up per-project infrastructure for #33/#34.

[argszero]

✅ LGTM — cycle #6

[argszero]

✅ LGTM — cycle #7

[argszero]

Superseded — merge conflicts from interleaved merges (#33). The multi-project evolution loop feature is re-implemented cleanly on top of merged master in the cycle #7 PR.