test(ai-chat): cover role-pick autoStart logic + the rolePickedNoSend reset (#149 review)

Review of #156 (Request changes) flagged the new CLIENT logic as untested. Extract
the decision logic from chat-thread.tsx into pure, unit-testable helpers and cover
both branches the reviewer called out:

- `roleLaunchMessage(role, default)` — the three-way handleRolePick behavior:
  autoStart=false -> null (send nothing); autoStart=true + custom -> trimmed
  message; autoStart=true + empty/null/whitespace -> default fallback.
- `shouldResetRolePicked(chatId, roleId, flag)` — the #149 render-phase reset; the
  regression test asserts the stuck-flag case (New chat after an autoStart=false
  pick -> cards return) that the pre-fix code never handled, and that a still-bound
  role keeps the cards hidden.

chat-thread.tsx now calls these helpers (behavior unchanged). 9 new pure tests.

Also folded the review's cosmetic suggestion: `x ? x : null` -> `x || null` in
ai-agent-roles.repo.ts (identical for string|null|undefined).

Client tsc clean; role-launch + role-cards green; repo spec green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/database/repos/ai-agent-roles/ai-agent-roles.repo.ts

@@ -96,7 +96,7 @@ export class AiAgentRoleRepo {
         enabled: values.enabled ?? true,
         autoStart: values.autoStart ?? true,
         // Empty string is treated as "no custom text" => null.
-        launchMessage: values.launchMessage ? values.launchMessage : null,
+        launchMessage: values.launchMessage || null,
       })
       .returningAll()
       .executeTakeFirst();
@@ -133,7 +133,7 @@ export class AiAgentRoleRepo {
     if (patch.autoStart !== undefined) set.autoStart = patch.autoStart;
     if (patch.launchMessage !== undefined) {
       // Empty string clears to null (client default launch message).
-      set.launchMessage = patch.launchMessage ? patch.launchMessage : null;
+      set.launchMessage = patch.launchMessage || null;
     }
     await db
       .updateTable('aiAgentRoles')