feat: Add authenticating step to ExecuteDrawer with enhanced UI

[Kenlachy]

• Add ExecuteDrawerStep type to types/index.ts
• Enhance authenticating step UI with spinner, anchor logo, and specific copy
• Show 'Proving wallet ownership to {anchorName}...' during SEP-10 auth
• Improve user understanding of Freighter authentication prompts

Addresses #25

Summary

Linked issue

Closes #

Changes

Testing notes

Automated

• npm run typecheck · ⏳ not run / ✅ green / ❌ failing
• npm run lint · ⏳ not run / ✅ green / ❌ failing
• npm run test · ⏳ not run / ✅ green / ❌ failing
• npm run build · ⏳ not run / ✅ green / ❌ failing

New / modified tests

Manual verification (if applicable)

Screenshots / recordings

Before	After

Checklist

Correctness

• The PR title follows Conventional Commits (auto-linted)
• One logical change; unrelated cleanup was split into a separate PR
• npm run typecheck passes
• npm run lint passes with zero new warnings (we run --max-warnings 0 in CI)
• npm run test passes; new behaviour has a test
• npm run build passes

Data integrity

• No fabricated rates, stub prices, or placeholder exchange rates (see issue.md #005)
• No isMock, // MOCK, // TODO: replace with real data, or commented-out real code
• If touching an anchor: the anchor's stellar.toml is publicly resolvable at https://{domain}/.well-known/stellar.toml and contains TRANSFER_SERVER_SEP0024
• If touching SEP-10: network passphrase assertion is intact (mainnet only)
• If touching SEP-24: the 10s AbortController timeout is intact on anchor fetches
• If touching the status poll: terminal states (completed | refunded | error) still stop the SWR loop

Security & non-custody (see docs/NON_CUSTODY.md once it lands)

• No new code path holds user keys, user funds, or long-lived anchor JWTs
• Every signing action is performed by the user's wallet (Freighter today)
• No secrets committed; .env.local is unchanged; new env vars are added to .env.example

Docs

• User-facing behaviour change → CHANGELOG.md entry under [Unreleased]
• API / schema change → relevant docs/*.md updated in the same PR
• Architecture change → docs/ARCHITECTURE.md updated (file map, diagram, or invariants as applicable)
• Public-facing feature → screenshot added to docs/showcase/images/ when relevant
• New env var → .env.example + README env table updated

Release hygiene

• If this touches a wave deliverable, the matching [ ] in docs/ROADMAP.md is updated
• No dependency added without justification in the PR description
• No breaking change hidden inside a non-breaking commit

Breaking changes

None.

For reviewers

Resolves #25

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