Add keyboard shortcuts system with reusable hint components

- Implement centralized keyboard registry with 20+ shortcuts
- Add instance navigation (Cmd+[1-9], Cmd+[/])
- Add session navigation (Cmd+Shift+[1-9], Cmd+Shift+[/])
- Add agent/model cycling (Tab, Cmd+Shift+M)
- Add input shortcuts (Cmd+P focus, Cmd+K clear, ↑↓ history)
- Add command palette (Cmd+Shift+P) with 8 MVP commands
- Implement message history per folder in IndexedDB (max 100)
- Create reusable Kbd and HintRow components
- Replace all keyboard hint rendering with consistent components
- Use text-based shortcuts (Cmd+Shift+M) for clarity

src/components/hint-row.tsx

@@ -0,0 +1,12 @@
+import { Component, JSX } from "solid-js"
+
+interface HintRowProps {
+  children: JSX.Element
+  class?: string
+}
+
+const HintRow: Component<HintRowProps> = (props) => {
+  return <span class={`text-xs text-gray-500 dark:text-gray-400 ${props.class || ""}`}>{props.children}</span>
+}
+
+export default HintRow