skip_kind matched SKIP_SUBSTRINGS as plain substrings, so 'xit(' hit
exit(, SystemExit( and process.exit(, and 'fit(' hit model.fit( and
profit(, flagging FLOOR SKIP on ordinary test-file lines (BLK-023). The
four bare identifiers (xit, fit, xdescribe, fdescribe) now match through
SKIP_IDENT_RE with an identifier-boundary lookbehind; the dotted and
decorator forms stay substrings. Flip-test fixtures cover the false
positive (RED before, GREEN after) and the three focus/skip calls.