Add bounty award and payout actions

[JustABiologist]

Closes #115.

This adds bounty payout actions to the governance bounty details view:

• active bounties now expose an "Award bounty" action that lets the curator enter the implementor/beneficiary address and submit api.tx.bounties.awardBounty(bountyId, beneficiary)
• pending-payout bounties now expose a "Claim payout" action once the payout unlock block has passed, submitting api.tx.bounties.claimBounty(bountyId)
• successful submissions refresh the displayed bounty details and use the existing wallet signing/toaster patterns

Verification:

• ./node_modules/.bin/tsc --noEmit --skipLibCheck
• git diff --check
• ./node_modules/.bin/tailwindcss -m -i ./styles/app.css -o app/styles/app.css
• ./node_modules/.bin/remix build

Note: ./node_modules/.bin/tsc --noEmit without --skipLibCheck is currently blocked by dependency declaration conflicts in the existing lockfile, including @polkadot/api-derive lookup exports, Remix DOM fetch types under Node 22, duplicate WebXR declarations, and remix-utils type exports. The app-level check passes with library checks skipped.