fix(cabinet-bin): align div_x source default with manifest

[aldoruizluna]

What changed

cabinet-bin/main.py:50: the PARAM fallback for div_x now equals the manifest default.

param	mode(s)	manifest default	source literal (before)	source literal (after)
div_x	bin, angled_bin, divided_bin	1	0	1

Direction and why

The source literal now follows the manifest default. Studio always sends the manifest-resolved set, so users already see 1. docs/README.md already documents 1. The default geometry does not change:

• Only divided_bin reads div_x.
• With 0 dividers, build_divided_bin already substituted one centred divider (x = 0).
• div_x = 1 places its single divider at -inner_w/2 + inner_w/2 = 0, the same wall.

How this maps to GOC-1

GOC-1 (Digital Twins MES, Phase 2) variables.json is only complete once yantra4d injects every declared parameter (RENDER_INJECT_FULL_PARAMS). This PR removes the default-drift note for this cartridge (rule from hyperobjects-spec#30), so turning that flag on cannot change this cartridge's geometry for callers that send {}.

Evidence

Run with hyperobjects-spec at 510efba (the #30 branch; CI pins 3ff3736, which lacks the rule), CadQuery 2.8.0, macOS:

$ y4d-spec check ./cabinet-bin
y4d-spec check: cartridges=1 failures=0 notes=0 ...            # before: notes=1 (default-drift div_x)

$ y4d-spec check ./cabinet-bin --render --require-openscad --parity --openscad-path libs --openscad-path .
  ok cabinet-bin (./cabinet-bin, 6 render(s) verified (3 preset), no comparable pair)
y4d-spec check: cartridges=1 failures=0 notes=0 geometry=verified renders=6 presets=3 skipped=0 parity=0/0 ok, warn=0, exempt=0, placement=0, failures=0

A green render on macOS does not prove the Linux render (AGENTS.md rule 4); the CI Linux render lane decides. That lane had not run when this was written. No verification change. One cartridge, one file.

CI status (updated)

Linux CI on this head: manifest conformance (all cartridges): pass; render (cartridges changed in this PR) (cabinet-bin): pass; render scope (which cartridges changed): pass.

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