story-kit: merge 277 - bot uses configured display_name

Adds system_prompt parameter to chat_stream so the Matrix bot
passes "Your name is {name}" to Claude Code. Reads display_name
from bot.toml config. Resolved conflicts by integrating bot_name
into master's permission-handling code structure.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/matrix/config.rs

@@ -49,6 +49,10 @@ pub struct BotConfig {
     /// backwards compatibility so existing bot.toml files still parse.
     #[allow(dead_code)]
     pub model: Option<String>,
+    /// Display name the bot uses to identify itself in conversations.
+    /// If unset, the bot falls back to "Assistant".
+    #[serde(default)]
+    pub display_name: Option<String>,
 }
 
 impl BotConfig {
@@ -265,6 +269,47 @@ history_size = 50
         assert_eq!(config.history_size, 50);
     }
 
+    #[test]
+    fn load_reads_display_name() {
+        let tmp = tempfile::tempdir().unwrap();
+        let sk = tmp.path().join(".story_kit");
+        fs::create_dir_all(&sk).unwrap();
+        fs::write(
+            sk.join("bot.toml"),
+            r#"
+homeserver = "https://matrix.example.com"
+username = "@bot:example.com"
+password = "secret"
+room_ids = ["!abc:example.com"]
+enabled = true
+display_name = "Timmy"
+"#,
+        )
+        .unwrap();
+        let config = BotConfig::load(tmp.path()).unwrap();
+        assert_eq!(config.display_name.as_deref(), Some("Timmy"));
+    }
+
+    #[test]
+    fn load_display_name_defaults_to_none_when_absent() {
+        let tmp = tempfile::tempdir().unwrap();
+        let sk = tmp.path().join(".story_kit");
+        fs::create_dir_all(&sk).unwrap();
+        fs::write(
+            sk.join("bot.toml"),
+            r#"
+homeserver = "https://matrix.example.com"
+username = "@bot:example.com"
+password = "secret"
+room_ids = ["!abc:example.com"]
+enabled = true
+"#,
+        )
+        .unwrap();
+        let config = BotConfig::load(tmp.path()).unwrap();
+        assert!(config.display_name.is_none());
+    }
+
     #[test]
     fn load_uses_default_permission_timeout() {
         let tmp = tempfile::tempdir().unwrap();