docs: Add Story Bible documentation to README

- Document Story Bible feature in the Tools section
- Add Story Bible to the reference material cross-reference
- Describe reference syntaxes (wiki-style and mention-style)
- Document highlighting and navigation features

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

README.md

@@ -202,7 +202,7 @@ In a project:
 * **Everything else is reference** — character sheets, the outline, the scratch
   pad — and is **not listed in the file panel**, which stays about the book.
   Reference material is reached through the windows that understand it
-  ([Characters](#characters-tools--characters), [Outline](#outline-tools--outline)),
+  ([Characters](#characters-tools--characters), [Story Bible](#story-bible-tools--story-bible), [Outline](#outline-tools--outline)),
   and it stays out of the order and out of the export.
 
   Turn on **View ▸ Show reference files** to list it in the tree anyway, dimmed,
@@ -330,6 +330,27 @@ it shows:
   changes; this one cannot. Long values are trimmed, since a grid is a
   quick-look summary.
 
+### Story Bible (Tools ▸ Story Bible…)
+
+The Story Bible window indexes all Story Bible items from your project's character,
+location, lore, and other reference directories. It supports:
+
+* Automatic indexing from directories like `03-Characters`, `02-Story Bible`,
+  `Characters`, `Locations`, `Lore`, etc.
+* Two reference syntaxes in your draft text:
+  - Wiki-style: `[[Character Name]]` or `[[John Doe]]`
+  - Mention-style: `@CharacterName` or `@John`
+* **Purple background highlighting** of Story Bible references in the editor
+* Click items in the Story Bible window to see all references to them in the current file
+* Click reference buttons to jump directly to that location in the editor
+* Metadata extraction from YAML frontmatter (id, title, type fields) or from filenames
+* Case-insensitive search and lookup
+
+Character sheets in the `Characters` folder are automatically indexed, and any
+markdown file with YAML frontmatter containing `id:` and `title:` fields will be
+included in the index. References in your draft text that match Story Bible items
+are highlighted and clickable.
+
 ### Outline (Tools ▸ Outline…)
 
 The snowflake outline files are scaffolds of HTML comments, one per beat