feat(local): model local command log boundary

Define local/offline truth as commands, domain events, and projections rather than stored DOM patches or EffectBatch payloads, and wire the techdemo through a local command-to-projection-to-effect flow.

req: local/001

req: local/002

req: local/003

req: local/004

req: examples/001

examples/techdemo/templates/control_center.heml

@@ -33,6 +33,7 @@
         <button type="button" data-hemx-handle="reset_demo">Reset demo</button>
       </div>
       <div data-hemx-slot="host_panel">{+= self.host =+}</div>
+      <div data-hemx-slot="local_panel">{+= self.local =+}</div>
       <p data-hemx-slot="notice" class="notice">Every control posts through a generated handle and receives typed updates.</p>
     </aside>