feat: add Shift+ modifier support for keybinds (#3679)

## Description:

This PR adds support for `Shift+<key>` keybind combinations across the
entire keybind system.

Previously, keybinds only supported a single key (e.g. `KeyB` for boat
attack). Now any keybind can be configured as `Shift+KeyB`, which will
only trigger when Shift is held down simultaneously.

Enables to use Shift + A for "select all" feature from #3677 

**Changes:**
- `InputHandler.ts`: Added `parseKeybind()` helper that parses
`"Shift+KeyB"` → `{ shift: true, code: "KeyB" }`. Added
`keybindMatchesEvent()` for consistent matching across all keyup/keydown
handlers. Updated `resolveBuildKeybind()` and all keybind comparisons to
respect the shift modifier.
- `SettingKeybind.ts`: When recording a keybind, lone modifier keys
(Shift, Ctrl, etc.) are skipped — the component waits for the actual
key. If Shift is held when the key is pressed, the value is stored as
`"Shift+<code>"`.
- `Utils.ts`: `formatKeyForDisplay()` now handles the `Shift+` prefix,
displaying e.g. `"Shift+B"`.
- `tests/InputHandler.test.ts`: Added 6 tests covering Shift+ keybind
matching, negative cases (plain key not triggering Shift-bound action),
coexistence of `Digit1` and `Shift+Digit1` on different actions, and
Numpad alias support with Shift.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## UI changes:

<img width="2255" height="2070" alt="CleanShot 2026-04-15 at 20 23
25@2x"
src="https://github.com/user-attachments/assets/96c19fc3-6294-40b7-82eb-3fde52b71618"
/>


## Please put your Discord username so you can be contacted if a bug or
regression is found:

fghjk_60845

src/client/UserSettingModal.ts

@@ -383,6 +383,26 @@ export class UserSettingModal extends BaseModal {
 
   private renderKeybindSettings() {
     return html`
+      <div
+        class="flex items-center gap-2 px-3 py-2 mb-3 rounded-lg bg-blue-500/10 border border-blue-500/20 text-blue-300/70 text-xs"
+      >
+        <svg
+          xmlns="http://www.w3.org/2000/svg"
+          class="h-3.5 w-3.5 shrink-0 opacity-70"
+          fill="none"
+          viewBox="0 0 24 24"
+          stroke="currentColor"
+        >
+          <path
+            stroke-linecap="round"
+            stroke-linejoin="round"
+            stroke-width="2"
+            d="M13 16h-1v-4h-1m1-4h.01M21 12a9 9 0 11-18 0 9 9 0 0118 0z"
+          />
+        </svg>
+        ${translateText("user_setting.keybinds_hint")}
+      </div>
+
       <h2
         class="text-blue-200 text-xl font-bold mt-4 mb-3 border-b border-white/10 pb-2"
       >