feat: show session name in statusline (#155)

* feat: show session name in statusline

Reads the session slug (auto-generated) and custom title (set via
/rename) from the transcript JSONL and displays it in dim text after
the project/git info on both expanded and compact layouts.

Custom title takes priority over auto-generated slug when both exist.

* test: add session name coverage and harden integration spawn

---------

Co-authored-by: Jarrod Watts <jarrod@cubelabs.xyz>

src/types.ts

@@ -72,6 +72,7 @@ export interface TranscriptData {
   agents: AgentEntry[];
   todos: TodoItem[];
   sessionStart?: Date;
+  sessionName?: string;
 }
 
 export interface RenderContext {