feat: Add wallet activity feed, sync job, dividend distribution, and multi-sig pause (#811, #818, #832, #826)

[chiscookeke11]

Summary of Changes

Consolidated resolution for Issues #811, #818, #832, and #826 under a single PR.

1. Issue #811: Unified Chronological Wallet Activity Feed

• Implemented GET /wallets/:address/activity?cursor=&limit= endpoint returning all on-chain events for a wallet.
• Enforced JWT validation matching :address (returns 401 when missing or mismatched).
• Aggregated across buys, sells, incoming/outgoing transfers, burns, and dividend payouts.
• Returns unified items formatted as { id, type, keyId, creatorName, amount, timestamp, txHash } sorted newest first.
• Supports cursor-based pagination (default 20, max 100) and returns empty array [] when no events exist.

2. Issue #818: Wallet Activity Sync Job for Transfers and Burns

• Implemented background streaming listener ActivitySyncJob parsing keys_transferred and keys_burned events.
• Writes dual records for keys_transferred (sender transfer_out, recipient transfer_in).
• Writes single record for keys_burned (burner burn).
• Built exponential backoff retry mechanism (up to 3 retries).
• Enforced idempotency on transaction hash txHash + actor + type.
• Added automatic reconnection on dropped stream.

3. Issue #832: Dividend Distribution Endpoint

• Added POST /creator/:keyId/dividends requiring key creator JWT authentication (403 for non-creators).
• Validated positive non-zero totalAmount (422 if 0 or negative).
• Checked creator XLM wallet balance before execution (400 if insufficient).
• Persisted DividendDistribution and calculated per-holder DividendClaim records.
• Returned { distributionId, totalAmount, holderCount, perKeyAmount }.

4. Issue #826: Multi-Sig Pause Coordination

• Added POST /admin/keys/:keyId/pause/propose requiring admin JWT to initiate a pause proposal and emit pause_proposal_created.
• Added POST /admin/keys/:keyId/pause/approve requiring a different admin JWT; rejects proposing wallet with 403.
• Approving admin executes pause, marks proposal executed, pauses trading on key, and emits trading_paused notification.
• 403 returned for non-admin callers on both endpoints.

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Linked Issues

Closes #811
Closes #818
Closes #832
Closes #826

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