feat(bazaar): track intent acceptances separately

[zubairz4far]

Follow-up to #20, based on the maintainer review.

Changes
Add a distinct intents_accepted counter for successful Bazaar accepts.
Keep swaps_completed and volume_usdc unchanged until settlement.
Expose intents_accepted through the reputation endpoint.
Add a backward-compatible DB migration for existing agent_history tables.
Update tests for both success and lock-failure paths.
Restore the explanatory comments requested in the #20 review.
Document the new acceptance accounting in the API docs.

This completes the remaining acceptance-accounting item from BRIDGE-08 / #15 without introducing settlement behavior.

[ericmt-98]

@zubairz4far — a heads-up about the GrantFox side, because right now your work here is not set up to be rewarded and I would rather tell you than let it pass silently.

GrantFox pays against a contributor application on the issue, not against the maintainer assigning you. You sent this PR without applying through the platform first, so on GrantFox the issue has no application attached — which means there is no record that can transition to COMPLETED and trigger a payout, even though the PR is merged. I tried assigning you from my side after the fact and it did not create one; that flow only works from the contributor's side.

The same applies to #29: it's a good follow-up and I asked for it, but it doesn't close a campaign issue, so as it stands it wouldn't be rewarded either.

Two things worth doing, if you want the work to count:

1. Check your GrantFox account for this project and see whether you can still apply against this issue, or ask GrantFox support if a completed one can be recorded retroactively. I can confirm from my side that the work was requested, reviewed and merged.
2. For anything future here — apply on the platform first, then open the PR. That's the order the payment path expects.

To be clear about what I think of the work: #20 was correct, minimal, and it left the settlement path documented for whoever picks it up. This is a platform-plumbing problem, not a quality one. Sorry it took a merge for me to spot it.