feat(sources): PDF-Upload auch in der Endkunden-App (Kundenquelle)

- POST /api/sources/upload-pdf: tenant-scoped Upload, gleiche Speicher-
  Konvention wie der Verwaltungs-Endpoint (<dirname(DB)>/pdfs/{sha}.pdf).
  Duplikat-Check beruecksichtigt globale Quellen.
- dashboard.html: +PDF-Button in der Quellenverwaltungs-Toolbar +
  eigenes Modal modal-pdf-upload (closeModal-Quotes via &#39;).
- app.js: App.openPdfUpload + _bindPdfUploadFormOnce (Submit nur einmal
  binden).
- api.js: API.upload(path, formData) Helper analog Verwaltung.

src/static/js/app.js

@@ -3106,6 +3106,70 @@ async handleRefresh() {
 
     _discoveredData: null,
 
+    openPdfUpload() {
+        const form = document.getElementById("pdf-upload-form");
+        if (form) form.reset();
+        const err = document.getElementById("pdf-upload-error");
+        if (err) { err.style.display = "none"; err.textContent = ""; }
+        const prog = document.getElementById("pdf-upload-progress");
+        if (prog) prog.style.display = "none";
+        openModal("modal-pdf-upload");
+        this._bindPdfUploadFormOnce();
+    },
+
+    _bindPdfUploadFormOnce() {
+        const form = document.getElementById("pdf-upload-form");
+        if (!form || form.dataset.bound === "1") return;
+        form.dataset.bound = "1";
+        form.addEventListener("submit", async (e) => {
+            e.preventDefault();
+            const errEl = document.getElementById("pdf-upload-error");
+            const progEl = document.getElementById("pdf-upload-progress");
+            const submitBtn = document.getElementById("pdf-upload-submit");
+            errEl.style.display = "none";
+
+            const fileInput = document.getElementById("pdf-upload-file");
+            const f = fileInput && fileInput.files && fileInput.files[0];
+            if (!f) {
+                errEl.textContent = "Bitte eine PDF-Datei auswaehlen.";
+                errEl.style.display = "block";
+                return;
+            }
+            if (f.size > 50 * 1024 * 1024) {
+                errEl.textContent = "Datei ueberschreitet 50 MB.";
+                errEl.style.display = "block";
+                return;
+            }
+
+            const fd = new FormData();
+            fd.append("file", f);
+            const nm = (document.getElementById("pdf-upload-name").value || "").trim();
+            if (nm) fd.append("name", nm);
+            fd.append("category", document.getElementById("pdf-upload-category").value || "sonstige");
+            const lng = (document.getElementById("pdf-upload-language").value || "").trim();
+            if (lng) fd.append("language", lng);
+            const nt = (document.getElementById("pdf-upload-notes").value || "").trim();
+            if (nt) fd.append("notes", nt);
+
+            submitBtn.disabled = true;
+            progEl.style.display = "block";
+            try {
+                await API.upload("/sources/upload-pdf", fd);
+                closeModal("modal-pdf-upload");
+                if (typeof UI !== "undefined" && UI.showToast) {
+                    UI.showToast("PDF hochgeladen -- Verarbeitung laeuft im Hintergrund", "success");
+                }
+                await App.loadSources();
+            } catch (err) {
+                errEl.textContent = err && err.message ? err.message : "Upload fehlgeschlagen";
+                errEl.style.display = "block";
+            } finally {
+                submitBtn.disabled = false;
+                progEl.style.display = "none";
+            }
+        });
+    },
+
     toggleSourceForm(show) {
         const form = document.getElementById('sources-add-form');
         if (!form) return;