Batch 246-A: the display side's register entry is the grounded one-creation-mode step

The window-synchronized (8.5.13) at the (8.5.4) states (MM.FLM86SDA.spanningDisplay_evenCocycle,
batch 244-A) is DISCHARGED.  The display side's registered open input is now the grounded
window-free one-creation-mode step, stated in the new file Definitions/MMFLM86ModeStepGrounded.lean
(MM.FLM86MSG.modeStepGrounded_zAligned_evenCocycle):

    (8.5.13) at (u, v) at any window  ==>  the GROUNDED (8.5.13) at each one-mode descendant pair
    (alpha_c(-r) u, v) and (u, alpha_c(-r) v):  some window K' at which it holds AND at or above
    which the (8.5.24) iterate family vanishes (the COMPLETE nonnegative iterate sum is the
    commutator).

Why the old entry fell (all landed):
  * the lattice corner is a THEOREM: unconditional at 0 <= <a,b> at every window (FLM (8.4.41)
    coefficientwise), batch 204-A residueNegativeAligned_evenCocycle at <a,b> < 0;
  * corollary851_lattice_of_canonical_le lifts the corner to every window past the canonical one
    (the iterate vanishes from the canonical window on, stateVanishesBelow_ZAligned);
  * the spanning induction over the (8.5.4) datum states (the batch-205/216 double List.induction,
    re-carried in the unbounded-window spelling: MM.FLM86MSG.spanningUnbounded_of_lattice_and_step);
  * the (8.10.5) finiteness grounds the final window
    (MM.FLM86MSG.spanningGroundedWindows_evenCocycle).

So the display side = corner (THEOREM) + the mode step (the ONE open input).  The step is the book's
own assembly: the descendant field is the normal-ordered product with the derivative factor (landed
Yzero_modeVL_eq_actionFamily), the commutator with Y(v,z_2) passes through it factor by factor (the
landed one-mode engine actionFamily_factorFactorZero_modeVL + the PROVED mode--field input
modeFieldCommInput8625), and the descendant's (8.5.24) iterate reindexes by the landed block
machinery (batches 233/240).  Landing it discharges the whole display side of Theorem 8.6.1.

New file: MM.FLM86MSG (11 declarations; the registered input carries the single sorry, guarded;
Corollary851ModeStepGrounded <=> Unbounded via (8.10.5) + of_cutoff, one direction proved).  SDA's
spanningDisplay_evenCocycle is now a theorem of the new input; its downstream consumers (the
(8.4.25) step, the commutator half, CCG's groundedZeroFace, the 8.6.1 file) are unchanged.

Registry after this batch: the mode step (display side) + negativeResidual_aligned ((8.8.41) l<0).

FinalCheck GREEN.  Docs: HANDOVER section 1 (new entry + row 1), README sorry map, NOTES section 146.
