fix(network): 🔒 trust user-installed CAs for custom/internal CA servers (#80)

Self-hosters fronting Calibre-web/OPDS/sync/AI with a private or internal
CA hit 'Trust anchor for certification path not found' because, on API 24+,
apps trust system CAs only by default — even when the device browser, which
trusts user-installed CAs, connects fine.

Add a network-security-config whose base-config trusts both system and user
CAs, applied app-wide. Every network path (OkHttp clients, Readium's
DefaultHttpClient) uses platform-default trust, so this single config covers
them all with no Kotlin changes. Fixed third-party public hosts
(openlibrary.org + covers) are pinned back to system-only so they don't
inherit the user-CA trust expansion.

cleartextTrafficPermitted is intentionally left unset: targetSdk 34 already
disables cleartext by default.

Closes #80

Author: vitofico

app/src/main/AndroidManifest.xml

@@ -12,6 +12,7 @@
         android:icon="@mipmap/ic_launcher"
         android:roundIcon="@mipmap/ic_launcher_round"
         android:label="@string/app_name"
+        android:networkSecurityConfig="@xml/network_security_config"
         android:theme="@style/Theme.Quire">
         <!-- configChanges keeps the Activity alive across rotation/keyboard/navigation
              changes. Required because EpubNavigatorFragment has no no-arg constructor:

app/src/main/res/xml/network_security_config.xml

@@ -0,0 +1,40 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  Trust user-installed CAs in addition to system CAs (issue #80).
+
+  Quire connects to arbitrary, user-configured servers (Calibre-web, OPDS,
+  sync, AI). Self-hosters commonly front those with a private/internal CA that
+  lives in the device's *user* CA store. On API 24+ apps trust system CAs only
+  by default, so without this Quire fails such servers with
+  "Trust anchor for certification path not found" even though the browser
+  (which does trust user CAs) connects fine.
+
+  This is a deliberate, bounded trust expansion appropriate for a self-hosted
+  app: only CAs the device owner installed themselves are honored, and modern
+  Android (11+) requires CA installation to go through Settings. The hosts can't
+  be enumerated at build time, so a global base-config is the only practical
+  option.
+
+  cleartextTrafficPermitted is intentionally left unset: with targetSdk 34 the
+  platform default already disables cleartext, so omitting it keeps current
+  behavior without hardcoding.
+
+  Fixed third-party public endpoints (Open Library metadata + covers) are pinned
+  back to system-only — they're served by public CAs and never need a private
+  CA, so they shouldn't inherit the user-CA trust expansion.
+-->
+<network-security-config>
+    <base-config>
+        <trust-anchors>
+            <certificates src="system" />
+            <certificates src="user" />
+        </trust-anchors>
+    </base-config>
+
+    <domain-config>
+        <domain includeSubdomains="true">openlibrary.org</domain>
+        <trust-anchors>
+            <certificates src="system" />
+        </trust-anchors>
+    </domain-config>
+</network-security-config>