feat: temporal trends CLI script + Dash tab (Task D.1)

D.1a: cli/compute_trends.py — standalone CLI that imports existing pipeline
functions to replay pathway computation for ~10 historical 6-month endpoints.
Creates pathway_trends table via CREATE TABLE IF NOT EXISTS.

D.1b: Trends tab (10th PP tab) with metric toggle (patients/cost/cost_pp_pa).
Query gracefully returns empty when table doesn't exist, figure shows
instruction message to run compute_trends.

dash_app/components/chart_card.py

@@ -14,6 +14,7 @@ TAB_DEFINITIONS = [
     ("network", "Network"),
     ("timeline", "Timeline"),
     ("doses", "Doses"),
+    ("trends", "Trends"),
 ]
 
 # Full set retained for Trust Comparison dashboard (Phase 10.8)
@@ -94,6 +95,23 @@ def make_chart_card():
                             ),
                         ],
                     ),
+                    # Trends metric toggle — visible only when trends tab active
+                    html.Div(
+                        id="trends-metric-wrapper",
+                        style={"display": "none"},
+                        children=[
+                            dmc.SegmentedControl(
+                                id="trends-metric-toggle",
+                                data=[
+                                    {"value": "patients", "label": "Patients"},
+                                    {"value": "total_cost", "label": "Cost"},
+                                    {"value": "cost_pp_pa", "label": "Cost p.a."},
+                                ],
+                                value="patients",
+                                size="xs",
+                            ),
+                        ],
+                    ),
                 ],
             ),
             # Chart area with loading spinner