fix: sync authotp and weighbridge custom fields via json fixtures

[av-dev2]

Summary

• 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, causing "Field authotp_validated not found" on Sales Invoice.
• Moved both the authotp fields and the standalone weighbridge Vehicle.default_tare_weight field 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 and weighbridge custom fields are created/synced correctly.
• pre-commit run --all-files passes.

[github-actions]

Backport failed for version-15, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin version-15
git worktree add -d .worktree/backport-136-to-version-15 origin/version-15
cd .worktree/backport-136-to-version-15
git switch --create backport-136-to-version-15
git cherry-pick -x 82dff79b1f1ff5da93ae4606042279806d27a404 9d843cb32ce143a6e2b47ef3bff9e4058ebdf0a6 2f750178b276b46cbf3696aba882accff450b957 59ee801286791648eb0a248cc09adeb7dae62c68 e2c436fedc83cdbb4859dc5ad9d3d20de5065c3d ab818e295d7199e6618f1a9762544e2ad1a1e332

[github-actions]

Backport failed for version-16-hotfix, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin version-16-hotfix
git worktree add -d .worktree/backport-136-to-version-16-hotfix origin/version-16-hotfix
cd .worktree/backport-136-to-version-16-hotfix
git switch --create backport-136-to-version-16-hotfix
git cherry-pick -x 82dff79b1f1ff5da93ae4606042279806d27a404 9d843cb32ce143a6e2b47ef3bff9e4058ebdf0a6 2f750178b276b46cbf3696aba882accff450b957 59ee801286791648eb0a248cc09adeb7dae62c68 e2c436fedc83cdbb4859dc5ad9d3d20de5065c3d ab818e295d7199e6618f1a9762544e2ad1a1e332