fix(background): Wave 2 - fix interrupt status checks, display text, error recovery grace, LSP JSONC

- fix(background): include "interrupt" status in all terminal status checks (3 files)
- fix(background): display "INTERRUPTED" instead of "CANCELLED" for interrupted tasks
- fix(cli): add error recovery grace period in poll-for-completion
- fix(lsp): use JSONC parser for config loading to support comments

All changes verified with tests and typecheck.

src/tools/background-task/create-background-task.ts

@@ -79,7 +79,7 @@ export function createBackgroundTask(manager: BackgroundManager): ToolDefinition
           }
           await delay(WAIT_FOR_SESSION_INTERVAL_MS)
           const updated = manager.getTask(task.id)
-          if (!updated || updated.status === "error") {
+          if (!updated || updated.status === "error" || updated.status === "cancelled" || updated.status === "interrupt") {
             return `Task ${!updated ? "was deleted" : `entered error state`}\.\n\nTask ID: ${task.id}`
           }
           sessionId = updated?.sessionID