feat(docx): Word (.docx) support via mammoth (lazy npm dependency)

makeDocxBook: the docx blob goes straight to mammoth.convertToHtml
(mammoth unzips internally; the browser entry takes {arrayBuffer}, the
node entry {buffer}). Converted HTML is sectioned at block-element
boundaries into ~150KB chunks (string-level — no DOMParser), giving a
Part N TOC; images inline as data URIs by default.

makeBook: zip files whose entries contain word/document.xml route to
the docx branch before the EPUB fallback (previously they died inside
new EPUB(...) on the missing container.xml).

mammoth is the fork's first runtime dependency: updates and security
fixes flow via semver; the browser-field mappings swap its node unzip
for the browser one; the dynamic import keeps it out of every other
format's path.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "foliate-js",
-  "version": "0.2.0",
+  "version": "0.3.0",
   "description": "Render e-books in the browser",
   "repository": {
     "type": "git",
@@ -43,5 +43,8 @@
     "dictd",
     "stardict",
     "opds"
-  ]
+  ],
+  "dependencies": {
+    "mammoth": "^1.13.0"
+  }
 }