chore: untrack 25 mars-genesis output fixtures + generalize internal-doc gitignore

The 25 JSON files under examples/mars-genesis/output/ are LLM run dumps
from April demo runs (1.4MB). They are not referenced by the README,
the cookbook, or any test, and were tracked by accident. .gitkeep keeps
the directory present for runs that still write here. Local copies are
untouched.

Generalize the internal-planning gitignore patterns from the previous
mars-genesis-specific rule to the full set called out in CLAUDE.md so
new planning docs (auth-v2-plan.md, PHASE_*, SESSION_*, etc.) cannot
slip into a published repo by default. Adds the matching docs/specs/,
docs/plans/, docs/internal/, docs/audits/ directories to the same
block.

Author: jddunn

.gitignore

@@ -28,9 +28,22 @@ coverage/
 *.sqlite-wal
 *.sqlite-shm
 
-# Superpowers
+# Internal planning content — never publish
 .superpowers/
 docs/superpowers/
+docs/specs/
+docs/plans/
+docs/internal/
+docs/audits/
+docs/STEP_*.md
+docs/PHASE_*.md
+docs/STAGE_*.md
+docs/SESSION_*.md
+docs/HANDOFF*.md
+docs/FINDINGS*.md
+docs/*-v[0-9]*-plan*.md
+docs/*-v[0-9]*-design*.md
+docs/*-plan-phase*.md
 
-# Internal planning docs (superpowers workflow)
-docs/mars-genesis-v*-plan*.md
+# Example run output — large LLM artifacts, not part of the published surface
+examples/*/output/*.json