Add basic-host and basic-server-react examples

Introduce new example implementations to replace simple-host and
simple-server:

- basic-host: Reference host implementation with double-iframe sandbox
  pattern for secure UI isolation (outer iframe validates and relays
  messages, inner iframe renders untrusted tool UI via srcdoc)

- basic-server-react: MCP server example demonstrating tool registration
  with linked UI resources and React UI using the useApp() hook

Build infrastructure updates:
- Add build:all script and simplify CI/pre-commit to use it
- Add examples:dev for watch-mode development workflow

Also change PostMessageTransport logging from info to debug level.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

examples/basic-host/src/index.module.css

@@ -0,0 +1,129 @@
+.callToolPanel, .toolCallInfoPanel {
+  margin: 0 auto;
+  padding: 1rem;
+  border: 1px solid #ddd;
+  border-radius: 4px;
+
+  * + & {
+    margin-top: 1rem;
+  }
+}
+
+.callToolPanel {
+  max-width: 480px;
+
+  form {
+    display: flex;
+    flex-direction: column;
+    gap: 1rem;
+  }
+
+  label {
+    display: flex;
+    flex-direction: column;
+    gap: 0.25rem;
+    font-weight: 600;
+  }
+
+  select,
+  textarea {
+    padding: 0.5rem;
+    border: 1px solid #ccc;
+    border-radius: 4px;
+    font-family: monospace;
+    font-size: inherit;
+  }
+
+  textarea {
+    min-height: 6rem;
+    resize: vertical;
+
+    &[aria-invalid="true"] {
+      background-color: #fdd;
+    }
+  }
+
+  button {
+    align-self: center;
+    min-width: 200px;
+    padding: 0.75rem 1.5rem;
+    border: none;
+    border-radius: 4px;
+    background-color: #1e3a5f;
+    font-size: inherit;
+    font-weight: 600;
+    color: white;
+    cursor: pointer;
+
+    &:hover:not(:disabled) {
+      background-color: #2d4a7c;
+    }
+
+    &:disabled {
+      opacity: 0.5;
+      cursor: not-allowed;
+    }
+  }
+}
+
+.toolCallInfoPanel {
+  display: flex;
+  gap: 1rem;
+  max-width: 1120px;
+  animation: slideDown 0.3s ease-out;
+}
+
+@keyframes slideDown {
+  from { opacity: 0; transform: translateY(-12px); }
+}
+
+.inputInfoPanel {
+  display: flex;
+  flex: 3;
+  flex-direction: column;
+  gap: 0.5rem;
+  min-width: 0;
+
+  .toolName {
+    margin: 0;
+    font-family: monospace;
+    font-size: 1.5rem;
+  }
+}
+
+.outputInfoPanel {
+  flex: 4;
+  min-width: 0;
+}
+
+.jsonBlock {
+  flex-grow: 1;
+  min-height: 0;
+  margin: 0;
+  padding: 1rem;
+  border-radius: 4px;
+  background-color: #f5f5f5;
+  overflow: auto;
+}
+
+.appIframePanel {
+  display: flex;
+  justify-content: center;
+  width: 100%;
+  min-height: 200px;
+
+  iframe {
+    flex-shrink: 0;
+    height: 100%;
+    max-width: 100%;
+    box-sizing: border-box;
+    border: 3px dashed #888;
+    border-radius: 4px;
+  }
+}
+
+.error {
+  padding: 1.5rem;
+  background-color: #ddd;
+  color: #d00;
+}