feat(sdk-svelte): match React Stellar hooks

[Hallab7]

sdk-svelte: parity with sdk-react hook set

Summary

Brings the Stellar API in @wraith-protocol/sdk-svelte to parity with the
current @wraith-protocol/sdk-react hook set using idiomatic Svelte stores and
actions.

This also adds a Svelte 5 receive example that derives a Stellar stealth
meta-address and scans recent on-chain announcements.

What changed

• Added useStellarAnnouncementScan
  • Exposes announcements, scanning, and error readable stores
  • Provides a scan(options) action backed by the core SDK's streaming
    announcement API
• Added useStellarSendStealthPayment
  • Exposes building and error readable stores
  • Provides a build(options) action
• Added useStellarBalance
  • Loads and exposes the native XLM balance through balance and loading
    stores
• Added useStellarName
  • Matches the React primitive's address, loading, and error shape
• Updated useStellarStealthKeys
  • Added the React-compatible generate(signature) action while preserving the
    existing deriveKeys action
  • Updated announcement fetching to use fetchAnnouncementsStream
• Exported all new primitives from the package entry point
• Enabled declaration generation so package consumers receive the updated public
  types
• Added @testing-library/svelte coverage with a rendered store subscriber to
  verify reactive updates
• Added examples/stellar-svelte-receive

Public API parity

React hook	Svelte primitive	State
useStellarStealthKeys	useStellarStealthKeys	keys, generate
useStellarAnnouncementScan	useStellarAnnouncementScan	announcements, scanning, error, scan
useStellarSendStealthPayment	useStellarSendStealthPayment	building, error, build
useStellarBalance	useStellarBalance	balance, loading
useStellarName	useStellarName	address, loading, error

All state fields are exposed as readable Svelte stores. Calling an action updates
the associated stores and notifies subscribers.

Example

The new stellar-svelte-receive Vite app demonstrates:

1. Parsing a 64-byte hexadecimal secret
2. Deriving Stellar stealth keys
3. Generating a shareable stealth meta-address
4. Scanning the configured Stellar deployment for announcements
5. Rendering scan progress, results, and errors reactively

Run it with:

pnpm --filter @wraith-protocol/sdk-svelte build
pnpm --filter @wraith-protocol/example-stellar-svelte-receive dev

Verification

• @wraith-protocol/sdk-svelte tests pass: 10/10
• Package typecheck passes
• Package ESM and declaration builds pass
• Example Svelte typecheck passes with no errors or warnings
• Example production build passes
• Vite dev server responds successfully and serves the compiled scan UI
• Store writes notify rendered Svelte subscribers
• Announcement scan state and results update reactively

Scope

Changes are limited to packages/sdk-svelte, the new
examples/stellar-svelte-receive app, and the required workspace lockfile
updates. No core SDK or unrelated package source was changed.

closes #129

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