Bug: `n(-1).` failed to parse — the tokenizer produced op `-`
followed by number `1`, and dl-pp-parse-arg expected a term after
seeing `-` as an op (and a `(` for a compound) but found a bare
number. Users had to write `(- 0 1)` or compute via `is`.
Fix: dl-pp-parse-arg detects op `-` directly followed by a number
token (no intervening `(`) and consumes both as a single negative
number literal. Subtraction (`is(Y, -(X, 2))`) and compound
arithmetic via the operator form are unaffected — they use the
`-(` lookahead path.
2 new parser tests: negative integer literal and subtraction
compound preserved.
Tokens → list of {:head :body} / {:query} clauses. SX symbols for
constants and variables (case-distinguished). not(literal) in body
desugars to {:neg literal}. Nested compounds permitted in arg
position for arithmetic; safety analysis (Phase 3) will gate them.
Conformance harness wraps lib/guest/conformance.sh; produces
lib/datalog/scoreboard.{json,md}.
