Review and clean up XXX comments in SkylineTool

SkylineTool has several XXX comments that need review:

**graphics.lisp:**
- Line 3138: XXX these are NTSC color names

**maps.lisp:**
- Line 78: XXX ref #109 (tileset comment)
- Line 286: XXX ref #109 (tileset comment)

**music.lisp:**
- Line 1406: NTSC XXX (duration calculation comment)

**fountain.lisp:**
- Line 80: XXX could use symbolic script IDs here for legibility

**decode-map.lisp:**
- Lines 57-58, 81: XXX undefined byte/bit comments

**forth.lisp:**
- Line 277: XXX unknown word comment

**decode-object.lisp:**
- Line 264: TODO: #1220 move these into JSON (already has issue number)

**lib/zpb-ttf/glyf.lisp:**
- Line 172: XXX flags debug output

These should be reviewed, converted to proper comments, or have issues created if they represent actual problems.