Add project-mode tooling: characters, outline, diff and revision status

Rounds out project mode, where the workspace is the project root and one
subfolder holds the manuscript proper:

- Characters and Outline windows, backed by new `characters` and `outline`
  modules that read the cast from character sheets and measure how much of
  the snowflake outline is actually written.
- Edit ▸ Changes… diffs the open file against its last committed version.
- Revision status, per-file and project word counts, an archive action and
  hidden folders in the file panel.
- Chapter-file export alongside the ODT master, richer header parsing, and
  a project word list for names and invented terms.
- The export path now follows the workspace: opening a project points it at
  that project root, keeping a file name you chose yourself and re-deriving
  one that merely echoed the folder it sat in.
- Clicking an issue in the grammar/spelling panel takes the editor to it,
  selecting the words and centring them; applying a suggestion jumps to the
  rewritten text as well.

README covers the new windows and workflows.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017bSn3Xijp8GofZVUnRX4oq

src/app/autocomplete.rs

@@ -26,7 +26,7 @@ impl App {
     /// Fold any new header field names from the current buffer into the list, so
     /// a field you just invented autocompletes without reopening the workspace.
     pub(super) fn merge_field_names_from_buffer(&mut self) {
-        let found = header_field_names(&self.buffer, &self.config.draft_marker);
+        let found = header_field_names(&self.document(), &self.config.draft_marker);
         let mut added = false;
         for f in found {
             if !self.field_names.iter().any(|n| n.eq_ignore_ascii_case(&f)) {