Implement UI scaling and more (#501)

**New Features**
 * Runtime font accessors and new symbol fonts for text, launcher, statusbar, and shared icons.
 * Added font height base setting to device.properties
 * Text fonts now have 3 sizes: small, default, large

**Improvements**
 * Renamed `UiScale` to `UiDensity`
 * Statusbar, toolbar and many UI components now compute heights and spacing from fonts/density.
 * SSD1306 initialization sequence refined for more stable startup.
 * Multiple image assets replaced by symbol-font rendering.
 * Many layout improvements related to density, font scaling and icon scaling
 * Updated folder name capitalization for newer style

Platforms/platform-posix/source/module.cpp

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: Apache-2.0
+#include <tactility/module.h>
+
+extern "C" {
+
+static error_t start() {
+    /* NO-OP for now */
+    return ERROR_NONE;
+}
+
+static error_t stop() {
+    /* NO-OP for now */
+    return ERROR_NONE;
+}
+
+// The name must be exactly "platform_module"
+struct Module platform_module = {
+    .name = "platform-posix",
+    .start = start,
+    .stop = stop,
+    .symbols = nullptr,
+    .internal = nullptr
+};
+
+}