Add title pages, standard manuscript format and collapsible panels

Five changes to the export and the window chrome:

* Manuscript details gains a contact field and a "Begin exports with a
  title page" option: the title, the author beneath it, and the contact
  details beneath that, laid out line for line as typed. A chapters +
  master export puts the title page on the master, not on each chapter.

* "Standard manuscript format" lays an export out the way an agent or an
  editor expects a submission: 12pt Courier, double-spaced, half-inch
  first-line indents, a Surname / Title / page header on every page but
  the title page, chapters opening a third of the way down, and `---`
  rendered as the conventional centred `#` scene break. The title page
  becomes the submission kind, with contact top-left and an approximate
  word count top-right. Off by default; margins were already the
  standard 1in on US Letter and are unchanged either way.

* A folder button beside Export ODT opens the project folder in the file
  manager -- the enclosing git work tree, including one still awaiting
  confirmation, since showing a folder is a smaller question than
  choosing which repository to commit to.

* The toolbar and the file list each collapse, from the pair of buttons
  at the right of the menu bar or from the View menu, and Ctrl+D folds
  both away together for distraction-free writing. Both choices persist.

* The editor sizes to its viewport instead of a fixed 30 rows, so the
  height a folded panel gives back reaches the page rather than leaving
  grey space below the text box that did not even take focus.

Two traps worth recording. ODF's style:master-page-name is inherited,
and any paragraph style carrying one forces a page break before every
paragraph that uses it -- a four-line contact block came out as four
pages until Contact_20_Line stopped inheriting from Contact_20_Block;
a test now pins which styles may carry one. And the status bar shares
a function with the toolbar, so guarding that function's top rather
than the top panel alone silently took the word counts away with it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GYSGPDwkSzhm4qLqjCbqxU

src/app/mod.rs

@@ -443,6 +443,11 @@ impl eframe::App for App {
             self.save_current();
         }
 
+        // Ctrl+D folds the panels away for distraction-free writing, and back.
+        if ctx.input(|i| i.modifiers.command && i.key_pressed(egui::Key::D)) {
+            self.toggle_distraction_free();
+        }
+
         // Ctrl+F opens find (search focused); Ctrl+H opens it focused on replace.
         if ctx.input(|i| i.modifiers.command && i.key_pressed(egui::Key::F)) {
             self.open_find(true);