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/lib/keyboard-registry.ts

@@ -0,0 +1,69 @@
+export interface KeyboardShortcut {
+  id: string
+  key: string
+  modifiers: {
+    ctrl?: boolean
+    meta?: boolean
+    shift?: boolean
+    alt?: boolean
+  }
+  handler: () => void
+  description: string
+  context?: "global" | "input" | "messages"
+  condition?: () => boolean
+}
+
+class KeyboardRegistry {
+  private shortcuts = new Map<string, KeyboardShortcut>()
+
+  register(shortcut: KeyboardShortcut) {
+    this.shortcuts.set(shortcut.id, shortcut)
+  }
+
+  unregister(id: string) {
+    this.shortcuts.delete(id)
+  }
+
+  get(id: string) {
+    return this.shortcuts.get(id)
+  }
+
+  findMatch(event: KeyboardEvent): KeyboardShortcut | null {
+    for (const shortcut of this.shortcuts.values()) {
+      if (this.matches(event, shortcut)) {
+        if (shortcut.context === "input" && !this.isInputFocused()) continue
+        if (shortcut.context === "messages" && this.isInputFocused()) continue
+
+        if (shortcut.condition && !shortcut.condition()) continue
+
+        return shortcut
+      }
+    }
+    return null
+  }
+
+  private matches(event: KeyboardEvent, shortcut: KeyboardShortcut): boolean {
+    const keyMatch = event.key.toLowerCase() === shortcut.key.toLowerCase()
+    const ctrlMatch = event.ctrlKey === (shortcut.modifiers.ctrl ?? false)
+    const metaMatch = event.metaKey === (shortcut.modifiers.meta ?? false)
+    const shiftMatch = event.shiftKey === (shortcut.modifiers.shift ?? false)
+    const altMatch = event.altKey === (shortcut.modifiers.alt ?? false)
+
+    return keyMatch && ctrlMatch && metaMatch && shiftMatch && altMatch
+  }
+
+  private isInputFocused(): boolean {
+    const active = document.activeElement
+    return (
+      active?.tagName === "TEXTAREA" ||
+      active?.tagName === "INPUT" ||
+      (active?.hasAttribute("contenteditable") ?? false)
+    )
+  }
+
+  getByContext(context: string): KeyboardShortcut[] {
+    return Array.from(this.shortcuts.values()).filter((s) => !s.context || s.context === context)
+  }
+}
+
+export const keyboardRegistry = new KeyboardRegistry()