fix: URL persistence in export + cache-busting v4.8.0

- getDocument() now explicitly lists all block fields including url
- loadDocument() initializes url/series_id for backward compat with older JSONs
- Cache-busting query params (?v=4.8) on all static assets
- PDF generator uses block.url directly (proper model field)
- Added 7 new URL tests (model, API, PDF link annotations)
- Version bumped to 4.8.0

tests/test_pdf.py

@@ -173,3 +173,60 @@ def test_generate_pdf_no_notes_single_page():
     pdf_bytes = generate_pdf(doc)
     pages = len(re.findall(rb'/Type\s*/Page[^s]', pdf_bytes))
     assert pages == 1, f"Expected 1 page, got {pages}"
+
+
+def test_generate_pdf_block_with_url_creates_link():
+    """Block with url should produce a clickable link annotation in PDF."""
+    import re
+    doc = make_doc(
+        blocks=[
+            Block(id="b1", date="2026-03-01", start="09:00", end="10:00",
+                  title="Linked Block", type_id="ws",
+                  url="https://example.com/test"),
+        ]
+    )
+    pdf_bytes = generate_pdf(doc)
+    assert pdf_bytes[:5] == b'%PDF-'
+    # Must contain a /URI annotation with the URL
+    uris = re.findall(rb'/URI\s*\(([^)]+)\)', pdf_bytes)
+    assert len(uris) == 1, f"Expected 1 URI annotation, got {len(uris)}"
+    assert uris[0] == b'https://example.com/test'
+    # Must have a Link subtype annotation
+    assert re.search(rb'/Subtype\s*/Link', pdf_bytes), "Missing /Subtype /Link annotation"
+
+
+def test_generate_pdf_block_without_url_no_link():
+    """Blocks without url should NOT produce link annotations."""
+    import re
+    doc = make_doc(
+        blocks=[
+            Block(id="b1", date="2026-03-01", start="09:00", end="10:00",
+                  title="No Link", type_id="ws"),
+        ]
+    )
+    pdf_bytes = generate_pdf(doc)
+    assert pdf_bytes[:5] == b'%PDF-'
+    uris = re.findall(rb'/URI\s*\(([^)]+)\)', pdf_bytes)
+    assert len(uris) == 0, f"Expected 0 URI annotations, got {len(uris)}"
+
+
+def test_generate_pdf_mixed_url_blocks():
+    """Only blocks with url should produce link annotations."""
+    import re
+    doc = make_doc(
+        blocks=[
+            Block(id="b1", date="2026-03-01", start="09:00", end="10:00",
+                  title="Has Link", type_id="ws",
+                  url="https://example.com/one"),
+            Block(id="b2", date="2026-03-01", start="10:00", end="11:00",
+                  title="No Link", type_id="ws"),
+            Block(id="b3", date="2026-03-01", start="11:00", end="12:00",
+                  title="Also Linked", type_id="ws",
+                  url="https://example.com/two"),
+        ]
+    )
+    pdf_bytes = generate_pdf(doc)
+    uris = re.findall(rb'/URI\s*\(([^)]+)\)', pdf_bytes)
+    assert len(uris) == 2, f"Expected 2 URI annotations, got {len(uris)}"
+    urls = sorted(u.decode() for u in uris)
+    assert urls == ['https://example.com/one', 'https://example.com/two']