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

TactilityKernel/source/concurrent/timer.c

@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: Apache-2.0
+#include <tactility/concurrent/timer.h>
+#include <tactility/check.h>
+#include <tactility/freertos/timers.h>
+#include <stdlib.h>
+
+struct Timer {
+    TimerHandle_t handle;
+    timer_callback_t callback;
+    void* context;
+};
+
+static void timer_callback_internal(TimerHandle_t xTimer) {
+    struct Timer* timer = (struct Timer*)pvTimerGetTimerID(xTimer);
+    if (timer != NULL && timer->callback != NULL) {
+        timer->callback(timer->context);
+    }
+}
+
+struct Timer* timer_alloc(enum TimerType type, TickType_t ticks, timer_callback_t callback, void* context) {
+    check(xPortInIsrContext() == pdFALSE);
+    check(callback != NULL);
+
+    struct Timer* timer = (struct Timer*)malloc(sizeof(struct Timer));
+    if (timer == NULL) {
+        return NULL;
+    }
+
+    timer->callback = callback;
+    timer->context = context;
+
+    BaseType_t auto_reload = (type == TIMER_TYPE_ONCE) ? pdFALSE : pdTRUE;
+    timer->handle = xTimerCreate(NULL, ticks, auto_reload, timer, timer_callback_internal);
+
+    if (timer->handle == NULL) {
+        free(timer);
+        return NULL;
+    }
+
+    return timer;
+}
+
+void timer_free(struct Timer* timer) {
+    check(xPortInIsrContext() == pdFALSE);
+    check(timer != NULL);
+    // MAX_TICKS or a reasonable timeout for the timer command queue
+    xTimerDelete(timer->handle, portMAX_DELAY);
+    free(timer);
+}
+
+error_t timer_start(struct Timer* timer) {
+    check(xPortInIsrContext() == pdFALSE);
+    check(timer != NULL);
+    return (xTimerStart(timer->handle, portMAX_DELAY) == pdPASS) ? ERROR_NONE : ERROR_TIMEOUT;
+}
+
+error_t timer_stop(struct Timer* timer) {
+    check(xPortInIsrContext() == pdFALSE);
+    check(timer != NULL);
+    return (xTimerStop(timer->handle, portMAX_DELAY) == pdPASS) ? ERROR_NONE : ERROR_TIMEOUT;
+}
+
+error_t timer_reset_with_interval(struct Timer* timer, TickType_t interval) {
+    check(xPortInIsrContext() == pdFALSE);
+    check(timer != NULL);
+    if (xTimerChangePeriod(timer->handle, interval, portMAX_DELAY) != pdPASS) {
+        return ERROR_TIMEOUT;
+    }
+    return (xTimerReset(timer->handle, portMAX_DELAY) == pdPASS) ? ERROR_NONE : ERROR_TIMEOUT;
+}
+
+error_t timer_reset(struct Timer* timer) {
+    check(xPortInIsrContext() == pdFALSE);
+    check(timer != NULL);
+    return (xTimerReset(timer->handle, portMAX_DELAY) == pdPASS) ? ERROR_NONE : ERROR_TIMEOUT;
+}
+
+bool timer_is_running(struct Timer* timer) {
+    check(xPortInIsrContext() == pdFALSE);
+    check(timer != NULL);
+    return xTimerIsTimerActive(timer->handle) != pdFALSE;
+}
+
+TickType_t timer_get_expiry_time(struct Timer* timer) {
+    check(xPortInIsrContext() == pdFALSE);
+    check(timer != NULL);
+    return xTimerGetExpiryTime(timer->handle);
+}
+
+error_t timer_set_pending_callback(struct Timer* timer, timer_pending_callback_t callback, void* context, uint32_t arg, TickType_t timeout) {
+    (void)timer; // Unused in this implementation but kept for API consistency if needed later
+    BaseType_t result;
+    if (xPortInIsrContext() == pdTRUE) {
+        check(timeout == 0);
+        result = xTimerPendFunctionCallFromISR(callback, context, arg, NULL);
+    } else {
+        result = xTimerPendFunctionCall(callback, context, arg, timeout);
+    }
+    return (result == pdPASS) ? ERROR_NONE : ERROR_TIMEOUT;
+}
+
+void timer_set_callback_priority(struct Timer* timer, enum ThreadPriority priority) {
+    (void)timer; // Unused in this implementation but kept for API consistency if needed later
+    check(xPortInIsrContext() == pdFALSE);
+
+    TaskHandle_t task_handle = xTimerGetTimerDaemonTaskHandle();
+    check(task_handle != NULL);
+
+    vTaskPrioritySet(task_handle, (UBaseType_t)priority);
+}