feat(frontend): show placeholder + hotkey tooltip on InputSearch trigger

The collapsed trigger is just a magnifier icon — there's no visible
hint about what it does or which key reveals it. Added a tooltip that
combines the `placeholder` with the platform-appropriate hotkey glyph
(⌘ on Apple, Ctrl elsewhere) using the existing `isMac()` helper. When
`hotkey` is `null` the suffix drops and the tooltip shows just the
placeholder.

Tooltip wraps only the trigger button: once the input is expanded the
caret is in it and a hovering tooltip would obscure the very thing the
user is typing into.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/ui/input-search.tsx

@@ -1,9 +1,11 @@
 import { Search } from 'lucide-react';
 import { motion } from 'motion/react';
-import { useCallback, useEffect, useRef, useState } from 'react';
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
 
 import { InputGroup, InputGroupAddon, InputGroupButton, InputGroupInput } from '@/components/ui/input-group';
+import { Tooltip, TooltipContent, TooltipTrigger } from '@/components/ui/tooltip';
 import { cn } from '@/lib/utils';
+import { isMac } from '@/lib/utils/platform';
 
 interface InputSearchProps {
     /** Accessible label for the trigger button + the input. */
@@ -58,6 +60,20 @@ export function InputSearch({
 
     const expand = useCallback(() => setIsExpanded(true), []);
 
+    // Hint shown over the collapsed trigger. The hotkey suffix mirrors the
+    // platform's modifier glyph (⌘ on Apple, Ctrl elsewhere) so the tooltip
+    // is actionable — the user sees the exact keys they can press without
+    // having to discover them by trial.
+    const tooltipText = useMemo(() => {
+        if (!hotkey) {
+            return placeholder;
+        }
+
+        const modifier = isMac() ? '⌘' : 'Ctrl';
+
+        return `${placeholder} (${modifier} ${hotkey.toUpperCase()})`;
+    }, [hotkey, placeholder]);
+
     // Focus the input the frame after it appears. `rAF` defers past the same
     // commit so motion's transform has started, otherwise focus can land on
     // a still-zero-width box and the user's caret blinks invisibly until the
@@ -175,15 +191,20 @@ export function InputSearch({
                         className="text-muted-foreground"
                     />
                 ) : (
-                    <InputGroupButton
-                        aria-label={ariaLabel}
-                        onClick={expand}
-                        size="icon-sm"
-                        type="button"
-                        variant="ghost"
-                    >
-                        <Search aria-hidden="true" />
-                    </InputGroupButton>
+                    <Tooltip>
+                        <TooltipTrigger asChild>
+                            <InputGroupButton
+                                aria-label={ariaLabel}
+                                onClick={expand}
+                                size="icon-sm"
+                                type="button"
+                                variant="ghost"
+                            >
+                                <Search aria-hidden="true" />
+                            </InputGroupButton>
+                        </TooltipTrigger>
+                        <TooltipContent>{tooltipText}</TooltipContent>
+                    </Tooltip>
                 )}
             </InputGroupAddon>
             <motion.div