feat: improve prompt - no spoilers, richer context annotations

Author: sedationh

app/src/main/java/com/example/epubspoon/service/FloatingService.kt

@@ -111,15 +111,19 @@ class FloatingService : Service() {
         floatingView = LayoutInflater.from(this).inflate(R.layout.layout_floating_button, null)
         updateProgressText()
 
+        // 获取屏幕宽度，默认放右上角
+        val displayMetrics = resources.displayMetrics
+        val screenWidth = displayMetrics.widthPixels
+
         val params = WindowManager.LayoutParams(
             WindowManager.LayoutParams.WRAP_CONTENT,
             WindowManager.LayoutParams.WRAP_CONTENT,
             WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY,
             WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
             PixelFormat.TRANSLUCENT
         ).apply {
-            gravity = Gravity.TOP or Gravity.END
-            x = 16
+            gravity = Gravity.TOP or Gravity.START
+            x = screenWidth - (72 * displayMetrics.density + 16 * displayMetrics.density).toInt()
             y = 300
         }
 
@@ -143,7 +147,7 @@ class FloatingService : Service() {
                 MotionEvent.ACTION_MOVE -> {
                     val dx = event.rawX - initialTouchX
                     val dy = event.rawY - initialTouchY
-                    if (dx * dx + dy * dy > 100) { // 移动超过 10px 判定为拖拽
+                    if (dx * dx + dy * dy > 100) {
                         isDragging = true
                     }
                     params.x = initialX + dx.toInt()

app/src/main/java/com/example/epubspoon/ui/MainActivity.kt

@@ -44,15 +44,21 @@ class MainActivity : AppCompatActivity() {
     private var floatingServiceRunning = false
 
     private val defaultInstruction = """
-You are my English reading assistant and cultural guide. I will send you passages from an English book one at a time.
+You are my English reading assistant and cultural guide. I will send you passages from an English book one at a time. I am reading this book for the first time.
+
+⚠️ **Critical rules:**
+- **NEVER spoil future plot, character fates, twists, or outcomes** — even indirectly. Do not hint at what will happen later.
+- **NEVER say things like** "this will be important later", "foreshadowing", "ironic given what happens next", or anything that reveals future events.
+- Only explain what is **in this passage and before it**. Treat every passage as if you don't know what comes after.
+- Your goal is to **enhance my reading experience** — help me fully understand what the author is expressing **right now**, without ruining the joy of discovery.
 
 For each passage, please go through it **sentence by sentence** in order. For each sentence, provide:
 
 1. **English original** — the sentence as-is.
 2. **Chinese translation** — natural, fluent Chinese translation.
 3. **Inline notes** — right after the translation, annotate as needed:
    - **word/phrase** — Chinese meaning；usage note or nuance if helpful.
-   - If a sentence involves **cultural references, historical allusions, religious/mythological context, social customs, literary devices, or implied meanings** that a Chinese reader might not immediately grasp, add a 💡 note explaining the cultural/contextual background in Chinese.
+   - If a sentence involves **cultural references, historical allusions, religious/mythological context, social customs, literary devices, or implied meanings** that a Chinese reader might not immediately grasp, add a 💡 note explaining the cultural/contextual background in Chinese. Focus on enriching understanding — explain what the author is conveying, the emotional undertone, rhetorical techniques, or real-world context that helps me appreciate the writing.
    - Not every sentence needs a 💡 note — only add when there's genuine cultural or contextual depth worth explaining.
 
 After all sentences are done, add: