refactor: replace chromedp with browser native print for PDF export

Remove chromedp dependency, use window.print() instead. Docker image no longer needs Chromium (~200MB smaller).

- Delete services/pdf.go and templates/reports/review.html

- Remove PDF API route POST /api/repos/:id/review/pdf

- Add @media print CSS to review page

- Remove chromium from Dockerfile

static/js/note-editor.js

@@ -149,55 +149,15 @@ const NoteEditor = {
     },
 
     /**
-     * Trigger PDF export and download.
+     * Trigger PDF export via browser's native print dialog.
+     * Users can select "Save as PDF" in the print dialog.
      */
-    async exportPDF() {
+    exportPDF() {
         if (!this.analysisId) {
             showToast('请先完成审查再导出 PDF', 'warning');
             return;
         }
-
-        const btn = document.getElementById('btn-export-pdf');
-        if (btn) {
-            btn.disabled = true;
-            btn.textContent = '⏳ 生成中...';
-        }
-
-        try {
-            const resp = await fetch(`/api/repos/${this.repoId}/review/pdf`, {
-                method: 'POST',
-                headers: { 'Content-Type': 'application/json' },
-                credentials: 'same-origin',
-                body: JSON.stringify({
-                    analysis_id: this.analysisId,
-                    base: document.getElementById('base-ref')?.value || '',
-                    head: document.getElementById('head-ref')?.value || '',
-                }),
-            });
-
-            if (!resp.ok) {
-                const err = await resp.json();
-                throw new Error(err.error || 'PDF generation failed');
-            }
-
-            // Download the PDF
-            const blob = await resp.blob();
-            const url = URL.createObjectURL(blob);
-            const a = document.createElement('a');
-            a.href = url;
-            a.download = `pr-helper-review-${new Date().toISOString().slice(0, 10)}.pdf`;
-            document.body.appendChild(a);
-            a.click();
-            document.body.removeChild(a);
-            URL.revokeObjectURL(url);
-        } catch (err) {
-            showToast('PDF 导出失败: ' + err.message, 'error');
-        } finally {
-            if (btn) {
-                btn.disabled = false;
-                btn.textContent = '📄 导出 PDF 报告';
-            }
-        }
+        window.print();
     },
 
     // ── Internal helpers ──────────────────────────────────────────