Add fuel temp and power trend lines to dashboard

src/reactor_sim/dashboard.py

@@ -43,6 +43,7 @@ class ReactorDashboard:
         self.quit_requested = False
         self.reset_requested = False
         self._last_state: Optional[PlantState] = None
+        self._trend_history: deque[tuple[float, float, float]] = deque(maxlen=120)
         self.log_buffer: deque[str] = deque(maxlen=4)
         self._log_handler: Optional[logging.Handler] = None
         self._previous_handlers: list[logging.Handler] = []
@@ -331,6 +332,7 @@ class ReactorDashboard:
         win.erase()
         win.box()
         win.addstr(0, 2, " Plant Overview ", curses.color_pair(1) | curses.A_BOLD)
+        self._update_trends(state)
         height, width = win.getmaxyx()
         inner_height = height - 2
         inner_width = width - 2
@@ -365,6 +367,12 @@ class ReactorDashboard:
                 ("Reactivity", f"{state.core.reactivity_margin:+.4f}"),
             ],
         )
+        left_y = self._draw_section(
+            left_win,
+            left_y,
+            "Trends",
+            self._trend_lines(),
+        )
         left_y = self._draw_section(left_win, left_y, "Key Poisons / Emitters", self._poison_lines(state))
         left_y = self._draw_section(
             left_win,
@@ -589,6 +597,24 @@ class ReactorDashboard:
         ]
         return lines
 
+    def _update_trends(self, state: PlantState) -> None:
+        self._trend_history.append((state.time_elapsed, state.core.fuel_temperature, state.core.power_output_mw))
+
+    def _trend_lines(self) -> list[tuple[str, str]]:
+        if len(self._trend_history) < 2:
+            return [("Fuel Temp Δ", "n/a"), ("Core Power Δ", "n/a")]
+        start_t, start_temp, start_power = self._trend_history[0]
+        end_t, end_temp, end_power = self._trend_history[-1]
+        duration = max(1.0, end_t - start_t)
+        temp_delta = end_temp - start_temp
+        power_delta = end_power - start_power
+        temp_rate = temp_delta / duration
+        power_rate = power_delta / duration
+        return [
+            ("Fuel Temp Δ", f"{end_temp:7.1f} K (Δ{temp_delta:+6.1f} / {duration:4.0f}s, {temp_rate:+5.2f}/s)"),
+            ("Core Power Δ", f"{end_power:7.1f} MW (Δ{power_delta:+6.1f} / {duration:4.0f}s, {power_rate:+5.2f}/s)"),
+        ]
+
     def _draw_health_bars(self, win: "curses._CursesWindow", start_y: int) -> int:
         height, width = win.getmaxyx()
         inner_width = width - 4