feat: add Notion-style breadcrumb navigation with dropdown menus

Backend:
- Added _nav_breadcrumb() to build page hierarchy chain (root → current)
- New /api/nav/menu endpoint returns workspace/folder children with has_children flag
- view_page() and view_page_root() now pass breadcrumb_items, nav_workspace_id, nav_page_id to template

Header template (_header.html):
- Replaced static breadcrumb with Alpine.js fdBreadcrumb() component
- Breadcrumb items now clickable with dropdown menus showing

tests/test_app.py

@@ -1847,3 +1847,70 @@ def test_gitea_private_pages_create_no_auth(client):
     """POST private-pages — 401 without session."""
     resp = client.post("/api/gitea/projects/owner/repo/private-pages", json={"title": "Test"})
     assert resp.status_code == 401
+
+
+# ── v2.6.0: Notion-style breadcrumb navigation ──
+
+def test_nav_menu_endpoint_responds(client):
+    """GET /api/nav/menu — always returns an items list (200)."""
+    resp = client.get("/api/nav/menu")
+    assert resp.status_code == 200
+    assert "items" in resp.json()
+
+
+def test_nav_menu_workspace_pages(client):
+    """/api/nav/menu returns root pages and nested children for a workspace."""
+    from app.db import get_conn
+    with get_conn() as conn:
+        u = conn.execute("INSERT OR IGNORE INTO users (login) VALUES ('navuser')")
+        uid = conn.execute("SELECT id FROM users WHERE login='navuser'").fetchone()["id"]
+        cur = conn.execute("INSERT INTO workspaces (name, owner_id) VALUES ('NavWS', ?)", (uid,))
+        ws_id = cur.lastrowid
+        p = conn.execute(
+            "INSERT INTO pages (workspace, workspace_id, title, content, content_format, "
+            "parent_section, parent_id) VALUES ('NavWS', ?, 'Parent Page', '', 'blocks', 'Private', NULL)",
+            (ws_id,),
+        )
+        parent_id = p.lastrowid
+        conn.execute(
+            "INSERT INTO pages (workspace, workspace_id, title, content, content_format, "
+            "parent_section, parent_id) VALUES ('NavWS', ?, 'Child Page', '', 'blocks', 'Private', ?)",
+            (ws_id, parent_id),
+        )
+        conn.commit()
+
+    # Root level should list the parent and flag it as having children
+    resp = client.get(f"/api/nav/menu?workspace_id={ws_id}")
+    assert resp.status_code == 200
+    items = resp.json()["items"]
+    names = {i["name"]: i for i in items}
+    assert "Parent Page" in names
+    assert names["Parent Page"]["has_children"] is True
+
+    # Children of the parent should include the child page
+    resp = client.get(f"/api/nav/menu?workspace_id={ws_id}&parent_id={parent_id}")
+    child_names = {i["name"] for i in resp.json()["items"]}
+    assert "Child Page" in child_names
+
+
+def test_page_renders_breadcrumb_data(client):
+    """Rendered page includes the breadcrumb JSON payload with a Home crumb."""
+    from app.db import get_conn
+    with get_conn() as conn:
+        conn.execute("INSERT OR IGNORE INTO users (login) VALUES ('crumbuser')")
+        uid = conn.execute("SELECT id FROM users WHERE login='crumbuser'").fetchone()["id"]
+        cur = conn.execute("INSERT INTO workspaces (name, owner_id) VALUES ('CrumbWS', ?)", (uid,))
+        ws_id = cur.lastrowid
+        p = conn.execute(
+            "INSERT INTO pages (workspace, workspace_id, title, content, content_format, "
+            "parent_section, parent_id) VALUES ('CrumbWS', ?, 'Crumb Page', '', 'blocks', 'Private', NULL)",
+            (ws_id,),
+        )
+        page_id = p.lastrowid
+        conn.commit()
+
+    resp = client.get(f"/pages/{page_id}")
+    assert resp.status_code == 200
+    assert 'id="fd-breadcrumb-data"' in resp.text
+    assert '"Home"' in resp.text
+    assert "fdBreadcrumb" in resp.text