feat: add Stellar wallet readiness preflight for demo flow

[codenerde]

Closes #174 Adds a comprehensive read-only wallet readiness preflight panel that checks:

• Freighter wallet extension reachability
• Wallet connection status
• Account presence
• Testnet network selection
• Account funding verification
• Horizon RPC health

The component shows actionable error messages with clear next steps for each failure scenario, making demo failures easier to diagnose. Preflight runs on testnet/demo environments and is visible before swap submission.

Closes #174

What & Why

One or two paragraph summary of the change and the problem it solves. Link the issue with Closes #… or Refs #….

Touched surface

Tick every layer this PR changes:

• frontend/ — React + Vite bridge UI
• packages/sdk/ — shared TypeScript SDK
• coordinator/ — order book + REST/WS service
• resolver/ — community resolver runner
• relayer/ — legacy v1 listener / watchdog (changes here need extra scrutiny)
• contracts/ — Solidity v2 (HTLCEscrow, ResolverRegistry)
• soroban/ — Stellar Soroban contracts (oversync-htlc, oversync-resolver-registry)
• docs/ — documentation only
• CI / config (.github/workflows/, docker, env.example)

Settlement & refund semantics

Critical for SCF / investor review. If any box is checked, the PR must also update docs/REVIEW_RESPONSE.md and link the updated section in the PR description.

• Bridge settlement semantics changed (claim path, timelock ordering, preimage handling, hashlock type, asset routing)
• Refund semantics changed (who can refund, who receives refunds, timelock values, refund-address pinning)
• Settlement-critical invariant changed (e.g. non-custodial guarantee, no-admin-escape-hatch, permissionless refund)
• None of the above — this PR cannot move, hold, or release user funds

Tests run

Tick the matches your change and paste the outcome below. Commands mirror the matrix in CONTRIBUTING.md.

• pnpm --filter @oversync/sdk build && pnpm --filter @oversync/sdk exec tsc --noEmit
• pnpm --filter @oversync/sdk test
• pnpm --filter @oversync/coordinator exec tsc --noEmit && pnpm --filter @oversync/coordinator test
• pnpm --filter @oversync/resolver exec tsc --noEmit && pnpm --filter @oversync/resolver test
• pnpm --filter @oversync/frontend exec tsc --noEmit && pnpm --filter @oversync/frontend test
• pnpm --filter @oversync/contracts compile && pnpm --filter @oversync/contracts exec hardhat test test/v2/HTLCEscrow.test.ts test/v2/ResolverRegistry.test.ts
• cd soroban && stellar contract build && cargo test --release
• (cd contracts && forge test --match-path "test/foundry/*" -v) (Solidity fuzz / invariant)
• pnpm test:e2e (cross-chain differential harness)
• node scripts/verify-addresses.mjs — required if addresses, configs, or env.example change
• node scripts/check-evidence-links.mjs — advisory; required if docs links change

Free-form outcome:

# commands actually run + result (all green / specific failures + how fixed)

UI / evidence artefacts

Required if the PR changes the frontend, observability, dashboards, or any docs that claim status, metrics, or addresses. Otherwise write n/a.

• Frontend visible change → screenshot or short clip attached (swap flow, refund dialog, history banner, wallet confirm)
• Coordinator API change → curl snippet + JSON response sample pasted below
• Metrics / KPI change → updated snapshot in docs/examples/metrics-snapshot.example.json (or new JSON in PR)
• Status table / README change → updated row(s) pasted below with the source link
• None of the above — no UI-observable artefact

Secrets, logging, and PII risk

• No secrets, private keys, RPC credentials, .env content, wallet mnemonics, or preimages added to the repo
• No new console.* / logger.* line that prints secrets, preimages, signed payloads, or PII
• No new Vite/build flag that exposes devtools output in production (the VITE_* and esbuild.drop policy still holds)
• None of the above — explain why this PR cannot be a secrets / logging risk:

Public proof links (SCF / investor evidence)

Only required for SCF tranche PRs or investor evidence packs. Otherwise write n/a.

• Sepolia Etherscan contract / tx link(s):
• Stellar Expert contract / tx link(s):
• Dashboard URL (coordinator /metrics, /health, public Grafana):
• CI run URL (https://github.com/karagozemin/OverSync/actions/runs/…):
• Screenshots, screen recordings, or PR-comment artefacts:

Breaking change & rollback

• Breaking change? Yes / No — describe caller impact, data migrations, revert safety:
• Migration or feature flag required? Yes / No — describe the path:

Reviewer checklist (for the PR author to self-verify)

• PR description and code comments are in English
• Linked issue or milestone
• No unrelated drive-by changes (reformatting, dep bumps, etc.)
• Tests touch the same files as the source change
• PR is reversible: a single git revert restores prior state

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[karagozemin]

Thanks for the Stellar wallet readiness preflight PR. I started the review under the karagozemin account, but the PR is blocked before frontend tests/build because whitespace validation fails in several touched files. Examples:

git diff --check origin/master...HEAD
frontend/src/components/BridgeForm.tsx:1172: trailing whitespace.
frontend/src/components/BridgeForm.tsx:1485: trailing whitespace.
frontend/src/components/StellarWalletPreflight.test.tsx:69: trailing whitespace.
frontend/src/components/StellarWalletPreflight.tsx:33: trailing whitespace.
frontend/src/hooks/useFreighter.ts:130: trailing whitespace.
frontend/src/lib/checkHorizonHealth.ts:3: trailing whitespace.

Please run a formatter or remove trailing whitespace across the PR, then rerun:

• git diff --check origin/master...HEAD
• pnpm --filter @oversync/frontend test -- --run frontend/src/components/StellarWalletPreflight.test.tsx
• pnpm --filter @oversync/frontend build

Once diff check is clean I can continue the functional review.