restructure repo for KiCad PCM packaging

Move plugin sources into plugins/ subdirectory, add 64x64 package
icon in resources/, and add metadata.json for PCM compatibility.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

metadata.json

@@ -0,0 +1,22 @@
+{
+  "$schema": "https://go.kicad.org/pcm/schemas/v1",
+  "name": "STM32 Pin Validator",
+  "description": "Validate STM32 pin assignments between KiCad and STM32CubeMX .ioc files",
+  "description_full": "Compares pin assignments across three sources:\n1. PCB layout (pad nets via pcbnew API)\n2. Schematic (pin names and labels, parsed from .kicad_sch)\n3. STM32CubeMX .ioc (GPIO signals and labels)\n\nResults are shown in a colour-coded table so mismatches are easy to spot. Handles pin remapping, aliases, and alternative GPIO names.",
+  "identifier": "stm32-pin-validator",
+  "type": "plugin",
+  "author": {
+    "name": "janik",
+    "contact": {
+      "git": "https://git.b4l.co.th/jamork/stm32PinValidator"
+    }
+  },
+  "license": "GPL-3.0-or-later",
+  "versions": [
+    {
+      "version": "1.0.0",
+      "status": "stable",
+      "kicad_version": "9.0"
+    }
+  ]
+}