chore(config): prune dead gitignore entries

Remove redundant and stale patterns:
- content-ron/, client-tmp/ — vanished dirs not referenced anywhere
- tooling/planet-gen/__pycache__/, sol_data/__pycache__/ — already
  covered by the global __pycache__/ pattern
- tooling/planet-gen/sol_data/.cache/ — already covered by .cache/
- db/commonwealth.db* — leftover guard from the pre-rename era;
  the stale on-disk file has been deleted

Also rewrite the misleading "Runtime databases (not tracked — created
on startup)" comment: server/data/systems.db is actually tracked, so
what the block really ignores are WAL/SHM sidecars plus the local-only
settings.db.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -1,7 +1,7 @@
 # Secrets
 .env
 
-# Runtime databases (not tracked — created on startup)
+# Local-only settings DB and WAL/SHM sidecars of tracked DBs
 server/settings.db
 server/settings.db-shm
 server/settings.db-wal
@@ -18,7 +18,6 @@ tooling/content-converter/target/
 tooling/econ-sim/target/
 tooling/line-previewer/target/
 tooling/test-client/target/
-content-ron/
 
 # Godot client
 client/.godot/
@@ -41,9 +40,6 @@ spikes/**/*.npy
 spikes/**/*.npz
 
 # Planet generator intermediates
-tooling/planet-gen/__pycache__/
-tooling/planet-gen/sol_data/.cache/
-tooling/planet-gen/sol_data/__pycache__/
 *.tmp.npz
 
 # Generated terrain grids (large, regenerated from pipeline)
@@ -55,9 +51,6 @@ docs/assets/downloads/
 # Reference repos for investigation
 vendor/
 
-# Database (shared across worktrees at ../settledreach.db, not tracked)
-db/commonwealth.db*
-
 # Frame0 ID mapping files (ephemeral, per-machine)
 *.idmap.json
 
@@ -82,5 +75,4 @@ Thumbs.db
 .claude/plans/
 .claude/projects/
 .claude/agent-memory/
-client-tmp/
 .tmp/