fix(interp): treat DECLARE parameter names as placeholders per QB45

fix(interp): treat DECLARE parameter names as placeholders per QB45

- bindScope no longer registers the argument cell under a DECLARE-only
  parameter name; only the definition's names bind, matching QB45 where
  DECLARE names are placeholders. The declared parameter still
  contributes its type (by-value cell kind, array/asTyped flags).
  Previously a name mismatch aliased locals to byref arguments
  (truth.bas teeslg's x2 wrote into its caller's x2); verified
  pixel-identical against QB.EXE in DOSBox. Adds regression test
  declareParameterNamesArePlaceholders.
- GameDriver gains --textdump/--textcell: TextDump recognizes each 8xN
  screen cell against the built-in CP437 VGA font into diffable text
  (custom glyphs get stable private-use code points), written wherever
  a $ screenshot lands or at end of run.