Titles are trimmed and truncated to 200 characters; language must be
blank or match ^[a-zA-Z0-9+#-]{1,40}$ (max 40 chars) or the create is
rejected with a clear 400. Regression tests cover truncation, malformed
and oversized language values, valid identifiers, and blank metadata.
GET ?password= and X-Paste-Password header checks in handleGetPaste were
unlimited (pentest2: 8 wrong = 8x401, no 429). Gate every password
verification on the same per-IP+paste unlock limiter (5/min, 429 with
Retry-After) already used by the POST unlock form path.
Regression tests: repeated wrong passwords via GET ?password= and via
header must eventually 429; correct password within burst still 200.
Fixes#81