fix(branding): use Wordmark SVG in FileSidebar and LandingPage

Replaces plain-text "Stirling PDF" renders with the <Wordmark>
component so brand surfaces stay consistent with AddFileCard.tsx.

frontend/src/core/components/shared/FileSidebar.css

@@ -50,12 +50,9 @@
 }
 
 .file-sidebar-brand-text {
-  font-family: "Alumni Sans", sans-serif;
-  font-weight: 700;
-  font-size: 18px;
-  letter-spacing: 0.3px;
-  color: var(--text-secondary);
-  white-space: nowrap;
+  height: 22px;
+  width: auto;
+  flex-shrink: 0;
 }
 
 /* ---- Search row ---- */

frontend/src/core/components/shared/FileSidebar.tsx

@@ -21,6 +21,7 @@ import { useFileHandler } from "@app/hooks/useFileHandler";
 import { useIndexedDB } from "@app/contexts/IndexedDBContext";
 import { accountService } from "@app/services/accountService";
 import { GoogleDriveIcon } from "@app/components/shared/CloudStorageIcons";
+import { Wordmark } from "@app/components/shared/Wordmark";
 import type { StirlingFileStub } from "@app/types/fileContext";
 import MenuIcon from "@mui/icons-material/Menu";
 import SearchIcon from "@mui/icons-material/Search";
@@ -334,9 +335,10 @@ const FileSidebar = forwardRef<HTMLDivElement, FileSidebarProps>(
           >
             <MenuIcon className="file-sidebar-menu-icon" />
             {!collapsed && (
-              <span className="file-sidebar-brand-text sidebar-content-fade">
-                Stirling PDF
-              </span>
+              <Wordmark
+                alt="Stirling PDF"
+                className="file-sidebar-brand-text sidebar-content-fade"
+              />
             )}
           </div>
 

frontend/src/core/components/shared/LandingPage.css

@@ -5,14 +5,11 @@
 
 /* ── Hero text ───────────────────────────────────────────── */
 .landing-title {
-  margin: 0;
-  margin-top: 1.75rem;
-  margin-bottom: 0.5rem;
-  text-align: center;
-  font-size: 2.125rem;
-  font-weight: 700;
-  letter-spacing: -0.02em;
-  color: var(--text-primary);
+  display: block;
+  margin: 1.75rem auto 0.5rem;
+  height: 3rem;
+  width: auto;
+  max-width: 100%;
 }
 
 .landing-subtitle {

frontend/src/core/components/shared/LandingPage.tsx

@@ -8,6 +8,7 @@ import MobileUploadModal from "@app/components/shared/MobileUploadModal";
 import { openFilesFromDisk } from "@app/services/openFilesFromDisk";
 import { LandingDocumentStack } from "@app/components/shared/LandingDocumentStack";
 import { LandingActions } from "@app/components/shared/LandingActions";
+import { Wordmark } from "@app/components/shared/Wordmark";
 import "@app/components/shared/LandingPage.css";
 
 const LandingPage = () => {
@@ -79,9 +80,10 @@ const LandingPage = () => {
       >
         <LandingDocumentStack />
 
-        <h1 className="landing-title">
-          {t("landing.heroTitle", "Stirling PDF")}
-        </h1>
+        <Wordmark
+          alt={t("landing.heroTitle", "Stirling PDF")}
+          className="landing-title"
+        />
         <p className="landing-subtitle">
           {t(
             "landing.heroSubtitle",