Add original generated portrait/icon artwork for every entry

Adds js/portraits.js: procedurally generated, original SVG artwork for
all 101 characters (a role-themed line-art medallion — sword for
swordsmen, crown for royalty, compass for navigators, etc., derived
from each character's role/epithet/affiliation) and all 58 Devil
Fruits (a stylized swirled-fruit icon colored by category with the
fruit's symbolic emoji at center).

Official One Piece artwork is copyrighted (Oda/Shueisha/Toei), so
rather than scraping and re-hosting character art from the web, every
image here is drawn from scratch with basic SVG primitives — no
external assets, no copyright risk, fully offline-capable, and crisp
at any size since it's vector.

Wires the new generators into every card and detail view: character
cards/profile header, Devil Fruit cards/detail header, the Devil-Fruit
callout on character pages, and user chips on Devil Fruit pages.
Removes the now-unused plain-letter initialFor() avatar helper.

index.html

@@ -62,6 +62,7 @@
 
     <script src="js/characters-data.js"></script>
     <script src="js/fruits-data.js"></script>
+    <script src="js/portraits.js"></script>
     <script src="js/app.js"></script>
     <script src="js/main.js"></script>
   </body>