feat: Support for multiple OPDS servers (#1209)

## Summary

* Add support for configuring and using multiple OPDS servers, replacing
the previous single-server limitation. Closes
https://github.com/crosspoint-reader/crosspoint-reader/issues/1178
* New OpdsServerStore singleton (modeled after WifiCredentialStore) that
persists up to 8 OPDS servers to /.crosspoint/opds.json with MAC-based
password obfuscation.
* One-time migration from legacy single-server fields in
CrossPointSettings to the new store on first boot.
* New OpdsServerListActivity for the device UI — works in two modes: a
settings list (add/edit/delete servers) and a picker (select which
server to browse). When only one server is configured, the picker is
skipped automatically.
* Renamed CalibreSettingsActivity → OpdsSettingsActivity for clarity. It
now edits individual OpdsServer entries (name, URL, username, password,
delete).
* OpdsBookBrowserActivity now receives an OpdsServer at construction and
uses its credentials for all fetches/downloads, and shows the server
name in the header.
* HttpDownloader::fetchUrl and downloadToFile accept optional per-call
username/password parameters instead of reading from global settings.
* REST API endpoints on CrossPointWebServer: GET /api/opds, POST
/api/opds, POST /api/opds/delete — passwords are never exposed over the
API (only a hasPassword flag), and omitting the password field on update
preserves the existing one.
* Web UI (SettingsPage.html) with dynamic OPDS server management cards —
add, edit, save, and delete servers from the browser.
<img width="932" height="906" alt="SCR-20260416-stvu"
src="https://github.com/user-attachments/assets/a8f18d84-4204-46a0-bb31-b73d24b3255f"
/>


## Additional Context

* The OpdsServerStore JSON format and obfuscation scheme are identical
to WifiCredentialStore, so the same JsonSettingsIO infrastructure
handles both.
* The web API uses POST /api/opds/delete instead of DELETE /api/opds
because the ESP32 WebServer doesn't support the DELETE method with a
request body.
* Existing single-server configurations are migrated automatically — no
user action required. After migration the legacy CrossPointSettings
fields are cleared so it only runs once.
* The HttpDownloader changes are backward-compatible: the credential
parameters default to empty strings, so existing callers are unaffected.

---

### 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? _**< YES >**_

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/activities/browser/OpdsBookBrowserActivity.cpp

@@ -7,7 +7,6 @@
 #include <OpdsStream.h>
 #include <WiFi.h>
 
-#include "CrossPointSettings.h"
 #include "MappedInputManager.h"
 #include "activities/network/WifiSelectionActivity.h"
 #include "activities/util/KeyboardEntryActivity.h"
@@ -123,7 +122,9 @@ void OpdsBookBrowserActivity::render(RenderLock&&) {
   const auto pageWidth = renderer.getScreenWidth();
   const auto pageHeight = renderer.getScreenHeight();
 
-  renderer.drawCenteredText(UI_12_FONT_ID, 15, tr(STR_OPDS_BROWSER), true, EpdFontFamily::BOLD);
+  // Show server name in header if available, otherwise generic title
+  const char* headerTitle = server.name.empty() ? tr(STR_OPDS_BROWSER) : server.name.c_str();
+  renderer.drawCenteredText(UI_12_FONT_ID, 15, headerTitle, true, EpdFontFamily::BOLD);
 
   if (state == BrowserState::CHECK_WIFI || state == BrowserState::LOADING) {
     renderer.drawCenteredText(UI_10_FONT_ID, pageHeight / 2, statusMessage.c_str());
@@ -179,18 +180,19 @@ void OpdsBookBrowserActivity::render(RenderLock&&) {
 }
 
 void OpdsBookBrowserActivity::fetchFeed(const std::string& path) {
-  if (strlen(SETTINGS.opdsServerUrl) == 0) {
+  if (server.url.empty()) {
     state = BrowserState::ERROR;
     errorMessage = tr(STR_NO_SERVER_URL);
     requestUpdate();
     return;
   }
 
-  std::string url = (path.find("http") == 0) ? path : UrlUtils::buildUrl(SETTINGS.opdsServerUrl, path);
+  std::string url = (path.find("http") == 0) ? path : UrlUtils::buildUrl(server.url, path);
+  LOG_DBG("OPDS", "Fetching: %s", url.c_str());
   OpdsParser parser;
   {
     OpdsParserStream stream{parser};
-    if (!HttpDownloader::fetchUrl(url, stream)) {
+    if (!HttpDownloader::fetchUrl(url, stream, server.username, server.password)) {
       state = BrowserState::ERROR;
       errorMessage = tr(STR_FETCH_FEED_FAILED);
       requestUpdate();
@@ -226,7 +228,7 @@ void OpdsBookBrowserActivity::fetchFeed(const std::string& path) {
 void OpdsBookBrowserActivity::navigateToEntry(const OpdsEntry& entry) {
   navigationHistory.push_back(currentPath);
   // Resolve to a full URL so sub-sub-navigation retains parent path context
-  const std::string feedUrl = UrlUtils::buildUrl(SETTINGS.opdsServerUrl, currentPath);
+  const std::string feedUrl = UrlUtils::buildUrl(server.url, currentPath);
   currentPath = UrlUtils::buildUrl(feedUrl, entry.href);
 
   state = BrowserState::LOADING;
@@ -259,18 +261,20 @@ void OpdsBookBrowserActivity::downloadBook(const OpdsEntry& book) {
   requestUpdate(true);
 
   // Build full download URL relative to the current feed, not the root server URL
-  const std::string feedUrl = UrlUtils::buildUrl(SETTINGS.opdsServerUrl, currentPath);
+  const std::string feedUrl = UrlUtils::buildUrl(server.url, currentPath);
   std::string downloadUrl = UrlUtils::buildUrl(feedUrl, book.href);
   std::string filename =
       "/" + StringUtils::sanitizeFilename(book.title + (book.author.empty() ? "" : " - " + book.author)) + ".epub";
   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) {
+  const auto result = HttpDownloader::downloadToFile(
+      downloadUrl, filename,
+      [this](const size_t downloaded, const size_t total) {
         downloadProgress = downloaded;
         downloadTotal = total;
         requestUpdate(true);
-      });
+      },
+      server.username, server.password);
 
   if (result == HttpDownloader::OK) {
     Epub(filename, "/.crosspoint").clearCache();
@@ -346,7 +350,6 @@ void OpdsBookBrowserActivity::checkAndConnectWifi() {
 }
 
 void OpdsBookBrowserActivity::launchWifiSelection() {
-  consumeBack = consumeConfirm = true;
   state = BrowserState::WIFI_SELECTION;
   requestUpdate();