feat: add systemMessage support for SessionStart hook and tune defaults

Add systemMessage field to HookResult so SessionStart can display a
colored timeline directly to the user in the CLI. The handler now
parallel-fetches both markdown (for Claude context) and ANSI-colored
(for user display) timelines, appending a viewer URL link.

Also update default settings to hide verbose token columns (read/work
tokens, savings amount) and disable full observation expansion, keeping
the cleaner index-only view by default.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/adapters/claude-code.ts

@@ -17,7 +17,11 @@ export const claudeCodeAdapter: PlatformAdapter = {
   },
   formatOutput(result) {
     if (result.hookSpecificOutput) {
-      return { hookSpecificOutput: result.hookSpecificOutput };
+      const output: Record<string, unknown> = { hookSpecificOutput: result.hookSpecificOutput };
+      if (result.systemMessage) {
+        output.systemMessage = result.systemMessage;
+      }
+      return output;
     }
     return { continue: result.continue ?? true, suppressOutput: result.suppressOutput ?? true };
   }