Add autosave draft system for partage form with HTMX-based session persistence

- New fragment endpoint POST/GET /partage/fragments/draft.php:
  saves all form fields to PHP session, excludes file/csrf/slug fields
  GET returns JSON for JS hydration on page load
  rotates both global CSRF and share CSRF tokens in sync

- form.php accepts optional $formExtraAttrs and $showAutosaveStatus:
  allows injecting HTMX attributes and 'Brouillon enregistré' indicator

- renderShareLinkForm adds hx-post with change/input debounce trigger,
  loads autosave-handler.js, hydrate fields from draft on page load

- Draft cleared on successful form submission in handleShareLinkSubmission

- autosave-handler.js now also updates share_link_token hidden input
  when rotating CSRF token (partage form uses both csrf_token and share_link_token)

- Added .autosave-status CSS to form.css (was admin.css-only)

- Updated fragment routing to accept GET requests (needed for draft hydration)

app/storage/schema.sql

@@ -87,6 +87,7 @@ CREATE TABLE IF NOT EXISTS theses (
     finality_id INTEGER,
     synopsis TEXT,
     context_note TEXT,
+    contact_visible TEXT DEFAULT NULL,
     remarks TEXT,
     access_type_id INTEGER,
     license_id INTEGER,
@@ -407,6 +408,7 @@ SELECT
     ft.name as finality_type,
     t.synopsis,
     t.context_note,
+    t.contact_visible,
     at.name as access_type,
     lt.name as license_type,
     t.license_id,