Keep the user's shift; trust the text guess less

- A tapped shift (on or off) survives the field re-reporting its context:
  it lasts until a character is typed, the hint changes or a field is focused
- An input-method reset forgets the guessed text and pending dead key, so
  double-space can't delete a character the keyboard never saw
- Fields that state typing preferences only get capitals if they ask
- Trackpad moves in fields without surrounding text make the guess unknown;
  Backspace removes a whole grapheme cluster from it

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/tst_controller.cpp

@@ -150,6 +150,46 @@ private Q_SLOTS:
         QCOMPARE(controller->shiftMode(), KeyboardController::ShiftMode::Once);
     }
 
+    void fieldHintsCanOptOutOfCapitalization()
+    {
+        TextContext context = Field;
+        context.hints = TextContext::AutoCompletion; // states preferences, no capitals among them
+        controller->setContext(context);
+        QCOMPARE(controller->shiftMode(), KeyboardController::ShiftMode::Off);
+        context.hints |= TextContext::AutoCapitalization;
+        controller->setContext(context);
+        QCOMPARE(controller->shiftMode(), KeyboardController::ShiftMode::Once);
+    }
+
+    void cursorMovesForgetTheGuessedText()
+    {
+        controller->resetContext(Field); // reports no text: we only know what we typed
+        for (const char *c : {"h", "i", "."})
+            tap(makeKey(KeyType::Character, QString::fromLatin1(c)));
+        controller->moveCursor({-2, 0}); // now somewhere inside "Hi."
+        tap(makeKey(KeyType::Space));
+        QCOMPARE(controller->shiftMode(), KeyboardController::ShiftMode::Off);
+    }
+
+    void contextReportKeepsTappedShift()
+    {
+        tap(makeKey(KeyType::Shift));
+        controller->setContext(MidSentence); // unchanged text, re-reported
+        tap(makeKey(KeyType::Character, u"a"_s));
+        QCOMPARE(engine.output, u"A");
+    }
+
+    void resetForgetsTextBefore()
+    {
+        TextContext context = MidSentence;
+        context.textBeforeCursor = u"word "_s;
+        controller->setContext(context);
+        controller->setContext(Field); // input-method reset: no surrounding text
+        tap(makeKey(KeyType::Space));
+        QCOMPARE(engine.output, u" ");
+        QCOMPARE(engine.mismatchedReplacements, 0);
+    }
+
     void doubleSpacePeriodCanBeTurnedOff()
     {
         controller->setOptions({.doubleSpacePeriod = false});