Harden AUR HTTP error matching against regex backtracking

[Copilot]

This change addresses the code scanning finding in the AUR update backoff path. The HTTP/status error detection used a single regex with ambiguous repetition; it now uses simple bounded patterns that preserve the existing 4xx/5xx detection intent without the ReDoS risk.

• AUR error classification

  • Replace the backtracking-prone stderr matcher in dot/src/commands/Updates.ts
  • Split detection into two explicit cases:
    • status ... 4xx/5xx
    • HTTP[/version] ... 4xx/5xx

• Behaviour preserved

  • Keep the existing backoff flow unchanged
  • Continue treating AUR failures as retryable only when the error output indicates HTTP 4xx/5xx conditions

const AUR_HTTP_FAILURE_PATTERNS = [
  /\bstatus\b[^0-9]*\b[45][0-9]{2}\b/i,
  /\bhttp(?:\/\d+(?:\.\d+)?)?\b[^0-9]*\b[45][0-9]{2}\b/i,
] as const;

AUR_HTTP_FAILURE_PATTERNS.some((pattern) => pattern.test(aurResult.stderr));