docs: complete JSDoc coverage for Stellar public API

[JohnOluB]

Closes #10
Adds full JSDoc to every public export from sdk/src/chains/stellar/. Every function has a 1–2 sentence summary, @param, @returns, @throws where applicable, a copy-pasteable @example block, and @see links to related functions. Types and interfaces have per-field documentation on all non-obvious fields. Constants carry semantic meaning beyond their literal values (e.g. the migration warning on STEALTH_SIGNING_MESSAGE).
Also sets up TypeDoc (typedoc.json + dev dependency) so npx typedoc generates clean reference HTML without errors — verifiable in the docs/stellar/ directory.
Checklist:

All public exports from sdk/src/chains/stellar have JSDoc matching the quality bar
npx typedoc generates clean reference HTML without errors
No TODO or FIXME in any new JSDoc
134/134 tests passing, build clean

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@JohnOluB Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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[truthixify]

Closing as duplicate. Issue #10 was addressed in #14 which landed first. Sorry for the duplicated effort — that's on us for assignment-tracking visibility.

Would love to keep your engagement though. A couple of nearby open Stellar Wave issues that fit a JSDoc/docs-quality contributor well:

• Stellar fetchAnnouncements time-range filtering #11 (time-range filtering for fetchAnnouncements) - already merged via feat: add Stellar announcement range scans #16
• CI-tested examples/ directory (Stellar-first) #22 (CI-tested examples/ directory, Stellar-first)
• React Native compatibility audit + fixes #19 (Bun + Deno runtime compatibility audit)

Pick anything that fits and ping me on the issue, I'll prioritize the review. Thanks @JohnOluB.