fix: share persistence + clipboard fallback + auto-save

- DB: pages.share_mode (private/invited/anyone) + published (bool)
- API: POST /board/api/share/{id} saves share settings to DB
- view_page: passes page_share_mode + page_published to template
- page_editor: inits share state from server, auto-saves on change
- Clipboard: fallback to textarea for HTTP (navigator.clipboard blocked)
- Toast: showToast() with proper timeout clearing

app/db.py

@@ -296,6 +296,14 @@ def init_db():
             conn.execute("ALTER TABLE pages ADD COLUMN deleted_at TEXT")
         except sqlite3.OperationalError:
             pass
+        try:
+            conn.execute("ALTER TABLE pages ADD COLUMN share_mode TEXT DEFAULT 'private'")
+        except sqlite3.OperationalError:
+            pass
+        try:
+            conn.execute("ALTER TABLE pages ADD COLUMN published INTEGER DEFAULT 0")
+        except sqlite3.OperationalError:
+            pass
         conn.commit()