fix bugs, harden server, strip-based dithering, update docs

Firmware:
- fix 90° rotation (was transpose)
- fix Adafruit_Thermal constructor (spurious DTR pin arg)
- wire up uploadImage; heatInterval now applied
- PSRAM-free strip dithering: 2-row buffers (~1KB) replace 153KB PSRAM alloc
- consolidate all pins into config.h; BUTTON_PIN → Config::PIN_BUTTON
- constrain contrast/brightness/heat in settings save handler
- uploadImage size param int → size_t

Server:
- canonicalize upload_dir at startup (fixes path traversal guard)
- path traversal guard in serve_image
- replace unwrap in gallery_data with error handling
- IMAGE_WIDTH/IMAGE_HEIGHT named constants

Gallery:
- innerHTML → createElement (XSS-safe)
- encodeURIComponent on image URLs
- replace("_"," ") → regex /_/g

Docs: rewrite README, clarify GUEST_MANUAL placeholders

include/config.h

@@ -2,16 +2,32 @@
 #include <Arduino.h>
 
 namespace Config {
-    // Hardware Pins (ESP32-CAM AI-Thinker)
-    constexpr int PIN_CAM_PWDN = 32;
-    constexpr int PIN_CAM_RESET = -1;
-    // ... (Add standard camera pins here to keep main clean) ...
-    
+    // Camera Pins (ESP32-CAM AI-Thinker)
+    constexpr int PIN_CAM_PWDN    = 32;
+    constexpr int PIN_CAM_RESET   = -1;
+    constexpr int PIN_CAM_XCLK   = 0;
+    constexpr int PIN_CAM_SIOD   = 26;
+    constexpr int PIN_CAM_SIOC   = 27;
+    constexpr int PIN_CAM_Y9     = 35;
+    constexpr int PIN_CAM_Y8     = 34;
+    constexpr int PIN_CAM_Y7     = 39;
+    constexpr int PIN_CAM_Y6     = 36;
+    constexpr int PIN_CAM_Y5     = 21;
+    constexpr int PIN_CAM_Y4     = 19;
+    constexpr int PIN_CAM_Y3     = 18;
+    constexpr int PIN_CAM_Y2     = 5;
+    constexpr int PIN_CAM_VSYNC  = 25;
+    constexpr int PIN_CAM_HREF   = 23;
+    constexpr int PIN_CAM_PCLK   = 22;
+
     // Printer Pins
-    constexpr int PIN_PRINTER_RX = 14; 
+    constexpr int PIN_PRINTER_RX = 14;
     constexpr int PIN_PRINTER_TX = 15;
-    
+
+    // Button
+    constexpr int PIN_BUTTON = 12;
+
     // Settings
-    constexpr int PRINTER_WIDTH = 384; 
     constexpr int BAUD_RATE = 9600; // Check your printer specs (some are 19200)
+    constexpr int PRINTER_SERIAL = 1;
 }