feat(ui): clickable document viewer — open any cited document in the browser from chat chips and the sources table

tests/e2e/test_chat_rag.py

@@ -98,10 +98,15 @@ def test_on_topic_question_streams_grounded_answer(
 
     # Grounded: a kubernetes.md source chip renders under the bubble
     # (top-N docs can add more chips; the question's doc must be among them).
+    # Phase 10: chips open the document viewer in a new tab (encoded URL).
     chip = page.locator(".msg.brain .source-chip", has_text="kubernetes.md")
     expect(chip).to_have_count(1)
     expect(chip.first).to_contain_text("kubernetes.md")
-    expect(chip.first).to_have_attribute("href", "/sources.html")
+    expect(chip.first).to_have_attribute(
+        "href", "/document.html?source=docs&path=homelab%2Fkubernetes.md"
+    )
+    expect(chip.first).to_have_attribute("target", "_blank")
+    expect(chip.first).to_have_attribute("rel", "noopener")
 
     # Button recovers: enabled + "Send" (never stale).
     expect(page.locator("#send-btn")).to_be_enabled()