feat: TFT display init and splash screen

Landscape 160x80 (rotation 3, no invert) per this panel.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

WeatherPredictor/WeatherPredictor.ino

@@ -1,6 +1,7 @@
 #include <Arduino.h>
 #include <Wire.h>
 #include "config.h"
+#include "display_ui.h"
 
 static void i2cScan() {
   Serial.println(F("I2C scan:"));
@@ -21,6 +22,9 @@ void setup() {
   Serial.println(F("\n=== Weather Predictor booting ==="));
   Wire.begin(I2C_SDA, I2C_SCL);   // MUST come before any I2C driver begin()
   i2cScan();
+
+  displayBegin();
+  displaySplash("Weather", "Predictor v0.1");
 }
 
 void loop() {

WeatherPredictor/display_ui.cpp

@@ -0,0 +1,27 @@
+#include <Adafruit_GFX.h>
+#include <Adafruit_ST7735.h>
+#include <SPI.h>
+#include "config.h"
+#include "display_ui.h"
+
+static Adafruit_ST7735 tft = Adafruit_ST7735(TFT_CS, TFT_DC, TFT_RST);
+
+void displayBegin() {
+  pinMode(TFT_BLK, OUTPUT);
+  digitalWrite(TFT_BLK, HIGH);           // backlight on
+  tft.initR(INITR_MINI160x80);           // 0.96" 80x160 ST7735S
+  tft.invertDisplay(false);               // this panel needs inversion; flip if colours look wrong
+  tft.setRotation(3);                    // portrait, 80 wide x 160 tall
+  tft.fillScreen(ST77XX_BLACK);
+}
+
+void displaySplash(const char* line1, const char* line2) {
+  tft.fillScreen(ST77XX_BLACK);
+  tft.setTextColor(ST77XX_WHITE);
+  tft.setTextSize(2);
+  tft.setCursor(4, 40);
+  tft.print(line1);
+  tft.setTextSize(1);
+  tft.setCursor(4, 70);
+  tft.print(line2);
+}

WeatherPredictor/display_ui.h

@@ -0,0 +1,5 @@
+#pragma once
+#include <Arduino.h>
+
+void displayBegin();
+void displaySplash(const char* line1, const char* line2);