Build a regular-expression matcher in the sandbox called regex_matcher.py.

It reads exactly two lines from standard input:
  line 1: a regex pattern
  line 2: a string to search

It must print:
  MATCH     if the pattern matches anywhere in the string (re.search semantics)
  NO_MATCH  otherwise
  ERROR     if the pattern is not a valid regex (e.g. an unbalanced bracket)

Python's re module is the reference — your matcher must behave identically to
`re.search` for the same inputs, including adversarial edge cases: empty
patterns, empty strings, escaped dots, character classes, quantifiers,
anchors, and INVALID regexes (which must print ERROR, not crash).

Test it against the examples in the verification oracle before replying DONE.
When the goal is met and verified, reply exactly: DONE.
