feat: Add runtime config, trusted senders, JMAP identities, and UI improvements

- Runtime environment variables for Docker-friendly configuration
- Trusted senders list for automatic image loading
- JMAP identities for proper sender address
- Improved email composer readability
- Horizontal scroll for wide HTML emails

locales/en/common.json

@@ -7,11 +7,18 @@
     "password_placeholder": "Enter your password",
     "sign_in": "Sign in",
     "signing_in": "Signing in...",
+    "loading": "Loading...",
     "error": {
       "invalid_credentials": "Invalid email or password",
       "connection_failed": "Failed to connect to the server",
       "generic": "An error occurred. Please try again."
-    }
+    },
+    "config_error": {
+      "title": "Configuration Error",
+      "fetch_failed": "Unable to load application configuration. Please try again later.",
+      "server_not_configured": "The mail server has not been configured. Please contact your administrator."
+    },
+    "remove_from_history": "Remove from history"
   },
   "sidebar": {
     "compose": "Compose",
@@ -82,6 +89,7 @@
     "hide_details": "Hide details",
     "external_content_warning": "Images and external content have been blocked",
     "load_external_content": "Load images",
+    "trust_sender": "Always trust this sender",
     "message_details": "Message Details",
     "authentication": {
       "title": "Authentication",
@@ -132,6 +140,7 @@
     "reply_to": "Reply",
     "reply_all_to": "Reply All",
     "forward_message": "Forward",
+    "from": "From",
     "to": "To",
     "cc": "CC",
     "bcc": "BCC",
@@ -139,7 +148,8 @@
     "body_placeholder": "Write your message...",
     "send": "Send",
     "cancel": "Cancel",
-    "attach": "Attach files",
+    "attach": "Attach",
+    "discard": "Discard",
     "discard_draft_confirm": "You have unsaved changes. Do you want to discard this draft?",
     "quote": {
       "reply_header": "On {{date}}, {{sender}} wrote:",
@@ -313,6 +323,25 @@
         "ask": "Always ask",
         "block": "Always block",
         "allow": "Always allow"
+      },
+      "trusted_senders": {
+        "label": "Trusted Senders",
+        "description": "Manage senders whose images load automatically",
+        "count_zero": "None",
+        "count_one": "1 sender",
+        "count_other": "{count} senders",
+        "modal_title": "Trusted Senders",
+        "empty_title": "No trusted senders yet",
+        "empty_description": "When viewing an email with blocked images, click \"Always trust this sender\" to add them here.",
+        "add_manually": "Add sender manually",
+        "add_button": "Add",
+        "add_placeholder": "Enter email address",
+        "search_placeholder": "Search senders...",
+        "no_results": "No senders match your search",
+        "remove": "Remove",
+        "close": "Close",
+        "invalid_email": "Please enter a valid email address",
+        "already_added": "This sender is already trusted"
       }
     },
     "composer": {