feat(draw): wire the drawing card into the conversation — end to end (T-318)

The last wire: a DrawingMessage conversation item + the Claude-extension
subscriber on the `draw` channel (buildSvgDocument → inject), the
conversation renderer (DrawingCard), the fold/summary switches, the i18n
`drawing` label, and registering `clide draw` at boot (empty template
registry for now — primitive SVG works; d2/icon/compare/image handlers
plug in as they land). `clide draw --file doc.json` now renders a card in
the conversation. Render widget-tested; analyze + format clean across the
repo. Templates + per-object overlay remain; the CHANGELOG entry lands
with the user-complete feature.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/src/daemon/draw_commands.dart

@@ -17,6 +17,8 @@ import 'dart:convert';
 
 import '../draw/draw_dispatch.dart';
 import '../draw/draw_doc.dart';
+
+export '../draw/draw_dispatch.dart' show DrawingFileReader, DrawingRegistry, DrawingTemplateHandler;
 import '../ipc/command_schema.dart';
 import '../ipc/envelope.dart';
 import '../ipc/schema_v1.dart';