fix: sync authotp and weighbridge custom fields via json fixtures (backport of #136, #137)

[av-dev2]

Summary

Manual backport of #136 and #137, since both branches' automatic backport attempts failed with cherry-pick conflicts.

• The authotp custom fields (Customer.authotp_validated, Sales Invoice.authotp*) were only created via after_install, so any site where av_tools was already installed before these fields were added never got them.
• Moved the authotp fields, the Vehicle.default_tare_weight field, and the weighbridge_ticket Link field on six Item child doctypes (Sales Invoice Item, Delivery Note Item, Sales Order Item, Purchase Order Item, Purchase Invoice Item, Purchase Receipt Item) into JSON fixtures under patches/custom_fields/custom_fields_json/, which the existing generic av_tools.utils.create_custom_fields.execute loader already runs on both after_install and after_migrate.
• Removed the now-redundant one-off patch scripts and their hook registrations, including a dead duplicate call in after_migrate.py.

Test plan

• Ran av_tools.utils.create_custom_fields.execute against an existing site with av_tools already installed; confirmed all authotp, Vehicle and weighbridge_ticket item fields are created/synced correctly.
• Pre-commit hooks pass on the changed files. Note: pre-commit run --all-files on this branch currently fails on pre-existing eslint errors in unrelated JS files this PR does not touch — this branch is behind version-15-hotfix on those lint fixes.