Auto-link Story Bible mentions in the draft, with a hover card to the entry

Bare proper nouns in prose ("Bixby walked in") now resolve against the
Story Bible automatically, the same as the existing [[wiki-links]] and
@mentions markup — no manual linking required. Matching is case-sensitive
and requires a capitalized, 3+ character match to a sheet's name or alias,
which is what keeps a character named "Hope" or "Will" from lighting up
on every unrelated use of the word; the longest phrase wins an overlap
("Bixby Reynolds" over "Bixby"), and a bare match never overrides the
author's own explicit markup.

Hovering a highlighted mention shows a card with the item's name, type
(Person/Place/Thing) and a summary (from a new summary:/description:
frontmatter field), with a link that opens the entry in the Story Bible
editor. The card appears after a short delay and stays open while the
pointer crosses onto it to reach the link.

Along the way:
- StoryBibleReference now carries absolute byte offsets (start/end) and
  the resolved item_id, replacing column/length, which were actually
  per-line and were being used as whole-buffer offsets — every reference
  past a file's first line highlighted and jumped-to in the wrong place.
  find_references() also now walks the buffer one char at a time rather
  than one byte, which could previously land mid-character and panic on
  any manuscript with accented letters or an em dash.
- build_story_bible_index() had its own, separately hardcoded list of
  Story Bible directory names that had drifted from
  find_story_bible_directory()'s list and no longer included
  03-Story-Bible, the bundled template's actual folder — so the index,
  and everything built on it, was silently empty for every project made
  from that template. It now reuses the one list.
- Story Bible Editor window: its tree and content ScrollAreas (and the
  content TextEdit) had no id_salt, so egui treated them as the same
  widget — fixed with explicit salts.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/story_bible_editor.rs

@@ -241,6 +241,7 @@ impl App {
                 
                 // Scroll area for tree
                 egui::ScrollArea::vertical()
+                    .id_salt("story_bible_editor_tree")
                     .auto_shrink(false)
                     .show(ui, |ui| {
                         if tree.is_empty() {
@@ -271,9 +272,11 @@ impl App {
                 
                 // Editor area
                 egui::ScrollArea::vertical()
+                    .id_salt("story_bible_editor_content")
                     .auto_shrink(false)
                     .show(ui, |ui| {
                         let text_edit = egui::TextEdit::multiline(&mut self.story_bible_editor_content)
+                            .id_salt("story_bible_editor_textedit")
                             .code_editor()
                             .desired_width(f32::INFINITY)
                             .desired_rows(20);