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/kbd.tsx

@@ -0,0 +1,54 @@
+import { Component, JSX, For } from "solid-js"
+import { isMac } from "../lib/keyboard-utils"
+
+interface KbdProps {
+  children?: JSX.Element
+  shortcut?: string
+  class?: string
+}
+
+const Kbd: Component<KbdProps> = (props) => {
+  const parts = () => {
+    if (props.children) return [{ text: props.children, isModifier: false }]
+    if (!props.shortcut) return []
+
+    const result: { text: string | JSX.Element; isModifier: boolean }[] = []
+    const shortcut = props.shortcut.toLowerCase()
+    const tokens = shortcut.split("+")
+
+    tokens.forEach((token, i) => {
+      const trimmed = token.trim()
+
+      if (trimmed === "cmd" || trimmed === "command") {
+        result.push({ text: isMac() ? "Cmd" : "Ctrl", isModifier: false })
+      } else if (trimmed === "shift") {
+        result.push({ text: "Shift", isModifier: false })
+      } else if (trimmed === "alt" || trimmed === "option") {
+        result.push({ text: isMac() ? "Option" : "Alt", isModifier: false })
+      } else if (trimmed === "ctrl") {
+        result.push({ text: "Ctrl", isModifier: false })
+      } else {
+        result.push({ text: trimmed.toUpperCase(), isModifier: false })
+      }
+    })
+
+    return result
+  }
+
+  return (
+    <kbd
+      class={`font-mono bg-gray-100 dark:bg-gray-800 px-1.5 py-0.5 rounded text-xs inline-flex items-center gap-0.5 ${props.class || ""}`}
+    >
+      <For each={parts()}>
+        {(part, index) => (
+          <>
+            {index() > 0 && <span class="opacity-50">+</span>}
+            <span>{part.text}</span>
+          </>
+        )}
+      </For>
+    </kbd>
+  )
+}
+
+export default Kbd