feat: port upstream PRs #852, #965, #972, #971, #977, #975

Port 6 upstream PRs (PR #939 was already ported):

- #852: Complete HalPowerManager with RAII Lock class, WiFi check in
  setPowerSaving, skipLoopDelay overrides for ClearCache/OtaUpdate,
  and power lock in Activity render task loops
- #965: Fix paragraph formatting inside list items by tracking
  listItemUntilDepth to prevent unwanted line breaks
- #972: Micro-optimizations: std::move in insertFont, const ref for
  getDataFromBook parameter
- #971: Remove redundant hasPrintableChars pre-rendering pass from
  EpdFont, EpdFontFamily, and GfxRenderer
- #977: Skip unsupported image formats before extraction, add
  PARSE_BUFFER_SIZE constant and chapter parse timing
- #975: Fix UITheme memory leak by replacing raw pointer with
  std::unique_ptr for currentTheme

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/hal/HalPowerManager.h

@@ -3,6 +3,7 @@
 #include <Arduino.h>
 #include <BatteryMonitor.h>
 #include <InputManager.h>
+#include <freertos/semphr.h>
 
 #include "HalGPIO.h"
 
@@ -10,6 +11,10 @@ class HalPowerManager {
   int normalFreq = 0;  // MHz
   bool isLowPower = false;
 
+  enum LockMode { None, NormalSpeed };
+  LockMode currentLockMode = None;
+  SemaphoreHandle_t modeMutex = nullptr;
+
  public:
   static constexpr int LOW_POWER_FREQ = 10;                    // MHz
   static constexpr unsigned long IDLE_POWER_SAVING_MS = 3000;  // ms
@@ -24,4 +29,20 @@ class HalPowerManager {
 
   // Get battery percentage (range 0-100)
   int getBatteryPercentage() const;
+
+  // RAII lock to prevent low-power mode during critical work (e.g. rendering)
+  class Lock {
+    friend class HalPowerManager;
+    bool valid = false;
+
+   public:
+    Lock();
+    ~Lock();
+    Lock(const Lock&) = delete;
+    Lock& operator=(const Lock&) = delete;
+    Lock(Lock&&) = delete;
+    Lock& operator=(Lock&&) = delete;
+  };
 };
+
+extern HalPowerManager powerManager;