Disable arrow substitutions in Overpass Mono

[devs6186]

Summary

• Disables Overpass Mono contextual arrow substitutions that collapse typed arrow sequences into single glyphs.
• Leaves mono text ligatures unchanged for the separate text-ligature issue-specific PR.
• Regenerates mono OTF, TTF, variable, and WOFF2 outputs.

Verification

• gftools builder sources/config_mono.yaml
• Focused HarfBuzz shaping check confirming ->, <-, <->, ^|, |v, and ^|v remain separate glyph sequences on representative mono TTF, OTF, and variable fonts.
• Scope check confirming upstream text ligatures still behave unchanged on this branch.

FontBakery note: the current upstream baseline is already red under the available WSL FontBakery environment. A local upstream-vs-change comparison during prep found no new FAIL or ERROR results introduced by the prepared changes.

Closes #94

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