feat: align portal center panel with side cards + redesign login page

- Portal: wrap .panel-head in matching card (border, radius, shadow) with
  cyan->purple left accent bar; h2 28px -> 20px; description right-aligned
  with vertical divider; top edge now aligns with side-menu & links-panel
- Login: switch from absolute-positioned icons to el-input prefix slot;
  layout brand row (logo + title + uppercase subtitle); add form-title
  section with gradient bar; consistent cyan focus; gradient button;
  dashed top divider for back-link; card width 420 -> 460
- Add .gitignore (node_modules, dist, __pycache__, .env, etc.)

.gitignore

@@ -0,0 +1,46 @@
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.egg-info/
+.venv/
+venv/
+env/
+.eggs/
+*.egg
+.pytest_cache/
+.mypy_cache/
+
+# Flask instance
+instance/
+*.db
+*.sqlite
+*.sqlite3
+
+# Logs
+*.log
+logs/
+
+# Node / Vite
+node_modules/
+dist/
+.vite/
+.cache/
+
+# Env / secrets
+.env
+.env.local
+.env.*.local
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+.DS_Store
+Thumbs.db
+
+# Misc
+.coverage
+htmlcov/
+.tox/