feat(text): plain-text (.txt) renderer

makeTextBook: UTF-8 decode (BOM stripped), blank-line paragraph split,
hard-wrapped lines joined (natural reflow under font-size changes), HTML
escaped, sections capped at ~150KB at paragraph boundaries (small Part N
TOC, avoids one giant DOM). Sections expose load/createDocument/size per
the reflowable interface; positions for txt books are percentage-based
(sections get fake CFIs from index, same as other non-EPUB books).

makeBook: dispatches text/plain or .txt in the final non-zip/non-pdf
branch. EPUB/PDF/CBZ/MOBI/FB2 routing untouched.

Tests: offline node harness (isText, paragraph join/split, escaping,
section capping, TOC shape, dispatch incl. zip-still-routes-to-EPUB).

package.json

@@ -1,6 +1,6 @@
 {
   "name": "foliate-js",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "description": "Render e-books in the browser",
   "repository": {
     "type": "git",