FE: features/bounties participant data layer (escrow client + hooks)

[0xdevcollins]

Context

Part of the Bounty Builder Lifecycle milestone (v1 boundless). The Configure epic's features/bounties/api/escrow-client.ts is organizer-only (participant escrow is explicitly out of scope there). This issue adds the builder/participant data layer to features/bounties/, reusing the shared escrow runner. Default funding mode MANAGED (custodial, no wallet signature) to mirror hackathon participant anchoring.

Blueprint to mirror

• features/hackathons/api/escrow-client.ts, use-escrow.ts (participant scope { kind: 'participant', ... }), use-submission-anchor.ts
• lib/wallet/wallet-kit.ts (signXdrWithKit) for the EXTERNAL fallback

Tasks

• features/bounties/api/participant-escrow-client.ts wrapping the participant REST surface: apply, submit, withdraw-application, withdraw-submission, contribute, ops poll, submit-signed.
• react-query hooks: useBountiesList/useBounty (public), useMyBountyApplication(bountyId) (applications/me), useApplyToBounty / useJoinCompetition / useEditApplication / useWithdrawApplication, useSubmitBounty / useWithdrawSubmission, useMyBountyActivity (apps + submissions). Drive escrow ops through useEscrowOpRunner (participant scope, default MANAGED).
• Types from the generated OpenAPI schema; run npm run codegen after the backend gap endpoints land.

Acceptance criteria

• Hooks typecheck against the generated schema; escrow ops drive the runner to terminal state.

Depends on

• Backend applications/me + participant dashboard queries (for the me/my-activity types via codegen).

[linear]

BOU-270

[coderabbitai]

🔗 Related PRs

#379 - Feat/abstract wallet [merged]
#425 - Participating page [merged]
#474 - Production [merged]
#488 - Pr 486 [merged]
#505 - Feat/improved rewards tab [merged]

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