Phase 1: add lazy node tree (Node/Element/Safe/Fragment/Media)

Introduce a FastHTML-style component model alongside the existing
function-based one, purely additive:

- Node: base renderable; __html__/__str__ render lazily so str()/f-string
  composition keeps working during migration.
- Element: the single class for any HTML element (tag + attrs + children),
  rendering via the existing memoized _render_element.
- Safe: wraps pre-rendered HTML (migration bridge for f-string components).
- Fragment: ordered children with no wrapper tag (replaces str(a)+str(b)).
- BaseComponent: base for higher-level components; render() returns a
  subtree, media declared via a Media attribute.
- Media: declarative JS deps with order-preserving dedup merge.
- collect_media()/render() helpers walk the tree.

The legacy Component() function now builds an Element and is Node-aware in
its child handling, so a tree mixing string- and node-returning components
renders correctly with byte-identical output. No call sites changed yet.

https://claude.ai/code/session_01BKurBhE3Qj25p7Bfsg7EeK

common/components/__init__.py

@@ -5,11 +5,19 @@ re-exports the public API so ``from common.components import X`` keeps working.
 """
 
 from common.components.core import (
+    BaseComponent,
     Component,
+    Element,
+    Fragment,
     HTMLAttribute,
     HTMLTag,
+    Media,
+    Node,
+    Safe,
     _render_element,
+    collect_media,
     randomid,
+    render,
 )
 from common.components.date_range_picker import (
     DateRangeCalendar,
@@ -82,7 +90,15 @@ from common.utils import truncate
 
 __all__ = [
     "truncate",
+    "BaseComponent",
     "Component",
+    "Element",
+    "Fragment",
+    "Media",
+    "Node",
+    "Safe",
+    "collect_media",
+    "render",
     "HTMLAttribute",
     "HTMLTag",
     "_render_element",