feat: Add central logging pragma (#843)

## Summary

* Definition and use of a central LOG function, that can later be
extended or completely be removed (for public use where debugging
information may not be required) to save flash by suppressing the
-DENABLE_SERIAL_LOG like in the slim branch

* **What changes are included?**

## Additional Context
* By using the central logger the usual:
```
#include <HardwareSerial.h>
...
  Serial.printf("[%lu] [WCS] Obfuscating/deobfuscating %zu bytes\n", millis(), data.size());
```
would then become
```
#include <Logging.h>
...
  LOG_DBG("WCS", "Obfuscating/deobfuscating %zu bytes", data.size());
```
You do have ``LOG_DBG`` for debug messages, ``LOG_ERR`` for error
messages and ``LOG_INF`` for informational messages. Depending on the
verbosity level defined (see below) soe of these message types will be
suppressed/not-compiled.

* The normal compilation (default) will create a firmware.elf file of
42.194.356 bytes, the same code via slim will create 42.024.048 bytes -
170.308 bytes less
* Firmware.bin : 6.469.984 bytes for default, 6.418.672 bytes for slim -
51.312 bytes less


### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _NO_

---------

Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

src/activities/browser/OpdsBookBrowserActivity.cpp

@@ -2,7 +2,7 @@
 
 #include <Epub.h>
 #include <GfxRenderer.h>
-#include <HardwareSerial.h>
+#include <Logging.h>
 #include <OpdsStream.h>
 #include <WiFi.h>
 
@@ -78,14 +78,14 @@ void OpdsBookBrowserActivity::loop() {
       // Check if WiFi is still connected
       if (WiFi.status() == WL_CONNECTED && WiFi.localIP() != IPAddress(0, 0, 0, 0)) {
         // WiFi connected - just retry fetching the feed
-        Serial.printf("[%lu] [OPDS] Retry: WiFi connected, retrying fetch\n", millis());
+        LOG_DBG("OPDS", "Retry: WiFi connected, retrying fetch");
         state = BrowserState::LOADING;
         statusMessage = "Loading...";
         updateRequired = true;
         fetchFeed(currentPath);
       } else {
         // WiFi not connected - launch WiFi selection
-        Serial.printf("[%lu] [OPDS] Retry: WiFi not connected, launching selection\n", millis());
+        LOG_DBG("OPDS", "Retry: WiFi not connected, launching selection");
         launchWifiSelection();
       }
     } else if (mappedInput.wasReleased(MappedInputManager::Button::Back)) {
@@ -265,7 +265,7 @@ void OpdsBookBrowserActivity::fetchFeed(const std::string& path) {
   }
 
   std::string url = UrlUtils::buildUrl(serverUrl, path);
-  Serial.printf("[%lu] [OPDS] Fetching: %s\n", millis(), url.c_str());
+  LOG_DBG("OPDS", "Fetching: %s", url.c_str());
 
   OpdsParser parser;
 
@@ -287,7 +287,7 @@ void OpdsBookBrowserActivity::fetchFeed(const std::string& path) {
   }
 
   entries = std::move(parser).getEntries();
-  Serial.printf("[%lu] [OPDS] Found %d entries\n", millis(), entries.size());
+  LOG_DBG("OPDS", "Found %d entries", entries.size());
   selectorIndex = 0;
 
   if (entries.empty()) {
@@ -351,7 +351,7 @@ void OpdsBookBrowserActivity::downloadBook(const OpdsEntry& book) {
   }
   std::string filename = "/" + StringUtils::sanitizeFilename(baseName) + ".epub";
 
-  Serial.printf("[%lu] [OPDS] Downloading: %s -> %s\n", millis(), downloadUrl.c_str(), filename.c_str());
+  LOG_DBG("OPDS", "Downloading: %s -> %s", downloadUrl.c_str(), filename.c_str());
 
   const auto result =
       HttpDownloader::downloadToFile(downloadUrl, filename, [this](const size_t downloaded, const size_t total) {
@@ -361,12 +361,12 @@ void OpdsBookBrowserActivity::downloadBook(const OpdsEntry& book) {
       });
 
   if (result == HttpDownloader::OK) {
-    Serial.printf("[%lu] [OPDS] Download complete: %s\n", millis(), filename.c_str());
+    LOG_DBG("OPDS", "Download complete: %s", filename.c_str());
 
     // Invalidate any existing cache for this file to prevent stale metadata issues
     Epub epub(filename, "/.crosspoint");
     epub.clearCache();
-    Serial.printf("[%lu] [OPDS] Cleared cache for: %s\n", millis(), filename.c_str());
+    LOG_DBG("OPDS", "Cleared cache for: %s", filename.c_str());
 
     state = BrowserState::BROWSING;
     updateRequired = true;
@@ -403,13 +403,13 @@ void OpdsBookBrowserActivity::onWifiSelectionComplete(const bool connected) {
   exitActivity();
 
   if (connected) {
-    Serial.printf("[%lu] [OPDS] WiFi connected via selection, fetching feed\n", millis());
+    LOG_DBG("OPDS", "WiFi connected via selection, fetching feed");
     state = BrowserState::LOADING;
     statusMessage = "Loading...";
     updateRequired = true;
     fetchFeed(currentPath);
   } else {
-    Serial.printf("[%lu] [OPDS] WiFi selection cancelled/failed\n", millis());
+    LOG_DBG("OPDS", "WiFi selection cancelled/failed");
     // Force disconnect to ensure clean state for next retry
     // This prevents stale connection status from interfering
     WiFi.disconnect();