chore(todo): split TODO.md into per-issue files under TODO/

Convert the flat TODO.md into a TODO/ folder where each GAL-N issue is
its own Linear-style markdown document with YAML frontmatter (id, title,
status, parent, labels), and add a README index grouped by section.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

TODO/GAL-27.md

@@ -0,0 +1,21 @@
+---
+id: GAL-27
+title: Different behaviors, points, and colors based on type
+status: Done
+parent: GAL-25
+labels: [enemy, gameplay]
+---
+
+# GAL-27: Different behaviors, points, and colors based on type
+
+Bosses are visually, behaviorally, and economically distinct from Grunts.
+
+## Acceptance criteria
+
+- [x] Colors differ (Grunt red, Boss purple) — `enemy.rs:80-83`
+- [x] Behaviors differ (Boss has `CaptureBeam`, distinct SwoopDive) — `enemy.rs:254-318`
+- [x] Points: Boss awards 300 points (3x Grunt) — `bullet.rs:13-14`
+
+## Comments
+
+- Completed on branch GAL-27, commit 98b74a7.