fix(desktop): resolve PortableGit for update checks + reserve titlebar tools space

- runGit() hardcoded spawn('git'), which ENOENTs on fresh installer-driven
  Windows installs (git is PortableGit under %LOCALAPPDATA%\hermes\git, never
  on PATH) — so "Check for updates" failed with "Couldn't check for updates".
  Add resolveGitBinary() mirroring findGitBash (PortableGit → Git-for-Windows
  → PATH) and use it in runGit.
- PageSearchShell rendered a full-width search input in the titlebar row, so
  on Windows its right edge slid under the fixed top-right tools + native
  window controls. Reserve that footprint via --titlebar-tools-* vars.

apps/desktop/src/app/page-search-shell.tsx

@@ -29,12 +29,22 @@ export function PageSearchShell({
       className={cn('flex h-full min-w-0 flex-col overflow-hidden bg-(--ui-chat-surface-background)', className)}
     >
       <div className="relative z-10 grid gap-2 border-b border-(--ui-stroke-tertiary) px-3 py-2.5">
-        <PageSearchInput
-          onChange={onSearchChange}
-          placeholder={searchPlaceholder}
-          trailingAction={searchTrailingAction}
-          value={searchValue}
-        />
+        {/* Reserve the top-right titlebar tools + native window-controls
+            footprint so the full-width search input never slides under them
+            (this header sits in the titlebar row at the window top). */}
+        <div
+          style={{
+            paddingRight:
+              'max(0px, calc(var(--titlebar-tools-right, 0px) + var(--titlebar-tools-width, 0px) - 0.75rem))'
+          }}
+        >
+          <PageSearchInput
+            onChange={onSearchChange}
+            placeholder={searchPlaceholder}
+            trailingAction={searchTrailingAction}
+            value={searchValue}
+          />
+        </div>
         {filters ? <div className="flex flex-wrap items-center justify-center gap-1.5">{filters}</div> : null}
       </div>
       <div className="min-h-0 flex-1 overflow-hidden bg-(--ui-chat-surface-background)">{children}</div>