feat(platform): migrate LCD assets to PNG and expand flash partitions

docs/architecture-and-flow-mermaid.md

@@ -192,7 +192,7 @@ flowchart LR
     PlatformReq["platform_lcd_request_presentation()"]
     Pending["lcd_direct pending request"]
     Render["cp_lcd_render loop"]
-    Draw["draw RLE asset frame\nfrom /littlefs/lcd"]
+    Draw["decode PNG asset frame\nfrom /littlefs/lcd"]
     Panel["ST7789 panel"]
 
     CP --> DomainReq --> Resolve --> Catalog --> PlatformReq --> Pending --> Render --> Draw --> Panel

docs/lcd-expressions.md

@@ -62,16 +62,18 @@ Transport disconnect/error events are not server error expressions.
 
 ## Asset Migration Direction
 
-The target image playback path is a platform-owned direct LCD asset pipeline.
-The reference project at `D:\Code\chaowan\lcd(1)\lcd` uses compiled RLE image
-arrays plus a small decoder/write path. When this is ported:
+The image playback path is a platform-owned direct LCD asset pipeline. Runtime
+PNG files are stored in the `gifpack` LittleFS partition, decoded through
+`lodepng`, converted to RGB565 in PSRAM, and written to the ST7789 panel through
+the existing bounded row-transfer buffer.
 
-- RLE decode and ST7789 writes stay inside `platform`.
+- PNG decode, the bounded four-entry LRU cache, and ST7789 writes stay inside
+  `platform`.
 - Domain continues to map semantic expressions to short asset IDs or names.
 - Upper layers continue to use `domain_runtime_request_expression()`.
-- Large image data should not be blindly compiled into the app if it risks
-  exceeding the OTA partition; prefer partition-backed resources for large
-  frame sets.
+- Runtime LCD assets must be added to the explicit PNG allowlist in
+  `components/platform/CMakeLists.txt`; files that only exist in the source
+  directory are not packaged automatically.
 
 ## Requesting Expressions