Fix README workflow badges

[manuelsampedro1]

Summary

• point README workflow links and shields at BitgesellOfficial/tbgl-v2 instead of the upstream keep-network/tbtc-v2 repository
• use the active bgl branch for badge status queries
• fix the Yearn badge query typo from vent=push to event=push

Validation

• rg -n "keep-network/tbtc-v2/actions|[?&]vent=|branch=main" README.adoc && exit 1 || true
• git diff --check

[MyTH-zyxeon]

Review-assist note for threshold-network#81 / tbgl-v2#1:

This looks like a legitimate docs/ops cleanup rather than formatting noise: the diff retargets the README workflow badges from the upstream keep-network/tbtc-v2 repo to BitgesellOfficial/tbgl-v2, switches the badge branch from main to bgl, and fixes the vent=push typo on the Yearn badge query.

Acceptance checks I would keep explicit before merge/payout:

• Confirm the referenced workflows actually exist in BitgesellOfficial/tbgl-v2 with those exact filenames (contracts.yml, typescript.yml, yearn.yml, system-tests.yml, monitoring.yml).
• Confirm bgl is the canonical active branch for badge status, so this does not silently point badges at a non-default or stale branch.
• Render the README once in GitHub UI and verify each badge/link resolves to the Bitgesell repo instead of the upstream Threshold/Keep pages.
• Treat this as a narrow documentation/maintainership improvement under the Bitgesell bounty lane, not as protocol/runtime work; if maintainers want higher-tier payout they should probably pair it with a more substantive test/CI fix rather than judge it as a major contribution by itself.

I did not run builds, install dependencies, connect wallets, start nodes, or perform any live-chain action. This is a maintainer-facing review checklist to help decide whether #1 should be accepted as a clean repo-ownership/docs fix.