Port display_gif_sd and display_speed_wifi to LVGL 9.6 + shared library

- both use shared/jc3636w518.ini, board library and perf monitor
- GIF decoded in the display color format, loop delay 1 ms,
  per-loop memory prints removed
- lv_conf: LVGL drive A: = SD card via LV_USE_FS_STDIO (/sdcard/)
- shared/README.md, CLAUDE.md and project README updated

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

shared/README.md

@@ -0,0 +1,60 @@
+# Shared JC3636W518 code
+
+Everything every JC3636W518 project needs, in one place:
+
+| Path | What |
+|---|---|
+| `jc3636w518.ini` | Common PlatformIO settings: pioarduino 51.03.05 (Arduino core 3.0.5), ESP32-S3 16 MB QIO / OPI PSRAM, `huge_app.csv`, `-O2`, LVGL 9.6.0, vendor display libraries, COM21 |
+| `include/lv_conf.h` | LVGL 9.6 config (generated from the 9.6 template; every change is marked `JC3636W518`) |
+| `include/lv_attr_jc3636w518.h` | LVGL attribute overrides: hot functions and `lv_display_flush_ready()` in IRAM |
+| `lib/JC3636W518/` | Board library: `jc3636w518.h` (display/touch/backlight init + LVGL glue), `pincfg.h` (pin map), `perf_monitor.h` (FPS/CPU monitor) |
+
+## New project
+```ini
+; platformio.ini
+[platformio]
+extra_configs = ../shared/jc3636w518.ini   ; path to this folder
+
+[shared]
+dir = ../shared                            ; same path
+
+[env:jc3636w518]
+extends = jc3636w518
+; project-specific overrides, e.g. board_build.partitions = default_16MB.csv
+```
+```cpp
+#include <Arduino.h>
+#include "jc3636w518.h"
+#include "perf_monitor.h"   // optional
+
+void setup() {
+  Serial.begin(115200);
+  lv_display_t *disp = scr_lvgl_init();   // also does lv_init()
+  perf_monitor_begin(disp);              // optional
+  // ... create LVGL UI ...
+}
+
+void loop() {
+  perf_timer_handler();                  // or lv_timer_handler()
+  vTaskDelay(1);
+  perf_monitor_print();                  // optional: FPS / refresh / other / CPU once per second
+}
+```
+Add `-DJC_DRAW_BUF_ROWS=<n>` to `build_flags` (as `${jc3636w518.build_flags}` + extra line) to change the draw buffer height (default 72).
+
+## Performance settings (measured with `display_gif_embedded`, 360×360 GIF at 23.7 fps)
+| Setting | Effect |
+|---|---|
+| LVGL 9.6 (AnimatedGIF decoder) | GIF decode 24 → 12 ms per frame vs LVGL 8.3 |
+| Two 72-row draw buffers in internal RAM | render while the previous chunk is sent (120 rows: no gain) |
+| `LV_COLOR_FORMAT_DEFAULT = RGB565_SWAPPED` | renders in the ST77916 byte order → no swap pass in flush |
+| QSPI 80 MHz (was 50) | faster transfer to the panel |
+| `-O2`, IRAM for hot LVGL functions | faster rendering/decoding |
+| GIF in display color format (`lv_gif_set_color_format`) | per sketch, only when the GIF needs no transparency (plain background) |
+
+Result: CPU for the GIF 86 % → 53 % at full frame rate.
+
+## Display / LVGL facts
+- Display format is `RGB565_SWAPPED`. For images/canvases you create yourself, use `lv_display_get_color_format(disp)` or ARGB8888 when transparency is needed.
+- LVGL drive `A:` = SD card (`LV_USE_FS_STDIO`, path `/sdcard/`); mount the card with `SD_MMC` first.
+- `LV_USE_STDLIB_MALLOC = CLIB`: LVGL uses `malloc`, so large allocations land in PSRAM. `lv_mem_monitor()` reports 0 in this mode.

shared/include/lv_conf.h

@@ -1957,14 +1957,14 @@
 #define LV_FS_DEFAULT_DRIVER_LETTER 0
 
 /** stdio */
-#define LV_USE_FS_STDIO 0
+#define LV_USE_FS_STDIO 1  /* JC3636W518: 'A:' = SD card (SD_MMC mount /sdcard) */
 
 #if LV_USE_FS_STDIO
 /** Drive letter for stdio (65 = 'A', 0 = disabled) */
-#define LV_FS_STDIO_LETTER 0
+#define LV_FS_STDIO_LETTER 'A'
 
 /** Working directory for stdio */
-#define LV_FS_STDIO_PATH ""
+#define LV_FS_STDIO_PATH "/sdcard/"
 
 /** Read cache size in bytes for stdio (0 = disabled) */
 #define LV_FS_STDIO_CACHE_SIZE 0