feat: resilient WS client, wallet views, sqlite maintenance, error-registry fee/rent

[Sendi0011]

Summary

Closes #372
Closes #363
Closes #362
Closes #371

This PR ships four scoped improvements together, tackling resilient task
streaming, wallet UX, on-disk data integrity, and sustainable error-record
accounting across the full stack.

• Design wallet views with copy-on-click, QR display, and balance chips #372 — Wallet views: copy-on-click address, QR display, and balance
  chips (native XLM + token balances) with full i18n.
• Add SQLite maintenance: WAL checkpointing, vacuum strategy, and backup job #363 — SQLite maintenance: WAL checkpointing, free-page vacuum, and
  scheduled online backups with retention.
• Introduce fee model and storage-rent accounting for error-registry #362 — Error-registry fee/rent: local persistence of the on-chain error
  lifecycle with TTL-based rent accounting, per-agent live-entry caps, and a
  deterministic expiry sweep.
• Make WebSocket client resilient with backoff and sequence-gap recovery #371 — WebSocket client resilience: auth handshake, heartbeat pong,
  seq-cursor resumption, gap detection with re-sync, and backoff.

Changes

#372 Wallet views (frontend)

• useWalletBalance now returns a full balances array (all Horizon asset
  types) alongside the backward-compatible native balance.
• WalletPage renders balance chips (native + token), with non-native tokens
  grouped under a "Tokens" heading; address copy uses a secure-context
  clipboard with execCommand fallback and shows a success toast.
• WalletWizard cash-out/fund step formats balances to 7 decimals and renders
  token chips, plus a "once funded…" hint and testnet faucet link.
• Added wallet.tokens.heading and a11y.balanceChip to en/zh and kept
  full parity. Updated WalletPage/WalletWizard tests.

#363 SQLite maintenance (backend)

• New src/services/dbMaintenance.ts: DbMaintenanceService runs a periodic
  pass across payments/tasks/agents/jobs DBs doing wal_checkpoint(TRUNCATE),
  incremental VACUUM above a free-page ratio, and online backup() snapshots
  with retention pruning.
• Wired into src/index.ts startup/shutdown and exposed the following config
  knobs: DB_MAINTENANCE_INTERVAL_MS, DB_MAINTENANCE_VACUUM_THRESHOLD,
  DB_BACKUP_DIR, DB_BACKUP_RETENTION_COUNT.

#362 Error-registry fee/rent (backend)

• New src/db/errorRegistry.ts: an errors table with TTL-based rent
  (expires_at), per-entry rentStroops attributed to a maintenance account,
  submit/resolve/countLiveByAgent/capLiveEntries/sweepExpired.
• Implemented the previously stubbed AgentDb.upsertError/resolveError and
  switched registry/sync.ts error handlers from log-only to persistence.
• New src/services/errorRegistryMaintenance.ts runs the deterministic expiry
  sweep and per-agent cap enforcement; wired into src/index.ts and config
  (ERROR_REGISTRY_MAINTENANCE_INTERVAL_MS, ERROR_REGISTRY_CAP_PER_AGENT).

#371 WebSocket client resilience (frontend)

• useTaskWebSocket now sends the { walletPublicKey } auth frame (opt-in),
  answers server ping with pong, tracks each event's seq, persists a
  per-task resume cursor, and reconnects with ?lastEventId=N so missed
  events are replayed.
• Detected seq gaps trigger one re-sync via the cursor; 4408 (STALE) closes
  reset the backoff for prompt reconnect; intentional disconnects no longer
  schedule a zombie reconnect.
• Added seq?: number to DAGEvent and optional maxReconnectAttempts /
  maxJitterMs (default 0 keeps the base backoff deterministic for tests).

Verification & Testing

• npm test (Backend/Frontend) — not run: node_modules not installed in
  this environment and the enclosing constraint forbids installing deps /
  running tests. Changes were reviewed for type consistency against the
  existing code and kept backward-compatible with the existing test
  expectations (deterministic backoff delays and attempt limits preserved).
• cargo test (Smart Contracts) — N/A: no smart-contract source changes.
• cargo fmt --check && cargo clippy (Contract Linting) — N/A.

Contributor Checklist

• PR title follows Conventional Commits (feat:)
• All CI checks pass locally — pending; please run backend npm run build
  / npm run lint and frontend npm run build to confirm (no deps here).
• Documentation updated in docs/ or README.md if applicable — new env
  knobs are self-documenting in src/config; happy to add to the operator
  guide if requested.
• No secrets or credentials committed

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