Chat bubbles, icons for chats, more vivid and distinct colour tags

- Bubbles: own messages right-aligned in their own colour, agent answers left.
- Chat icons (22, validated on the server), shown in list, top bar, project page.
- Colour tags: eight fixed hues (new: pink) with theme-matched lightness and the
  highest chroma sRGB allows; stronger background tint.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

core/src/types.rs

@@ -193,10 +193,19 @@ pub struct Session {
     /// Colour tag of the chat (a palette name, see `SESSION_COLORS`); the client maps it to the theme.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub color: Option<String>,
+    /// Icon of the chat (a name from `SESSION_ICONS`), shown in the list and the top bar.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub icon: Option<String>,
 }
 
 /// Names of the colour tags: the client draws them with the colours of the active theme.
-pub const SESSION_COLORS: &[&str] = &["red", "orange", "yellow", "green", "aqua", "blue", "purple"];
+pub const SESSION_COLORS: &[&str] = &["red", "orange", "yellow", "green", "aqua", "blue", "purple", "pink"];
+
+/// Icons a chat can get (names of the client's icon set).
+pub const SESSION_ICONS: &[&str] = &[
+    "robot", "brain", "terminal", "wrench", "gear", "chart", "shield", "image", "music", "cube", "file-text", "folder", "search", "sparkle", "clock", "lock",
+    "users", "toolbox", "plug", "scroll", "eye", "template",
+];
 
 impl Session {
     pub fn clean_room(&self, default: bool) -> bool {