docs: add stellar cryptography architecture page

[emarkees]

Closes #22

---

Description

This PR introduces the Stellar Cryptography Architecture documentation page (docs/architecture/stellar-cryptography.mdx). It serves to bridge the gap between the @wraith-protocol/sdk code and the cryptographic rationale behind it, allowing auditors and contributors to fully understand the protocol's stealth payment mechanisms on Stellar without having to reverse-engineer the source.

Changes Included

• New Architecture Page: Created stellar-cryptography.mdx which maps high-level cryptographic concepts directly to their specific sdk/chains/stellar/* implementations.
• Navigation Update: Registered the new page in docs.json under the Architecture navigation group.

Cryptographic Concepts Covered

• Curve Selection: Explains the reliance on ed25519 over secp256k1 for Stellar network compatibility.
• ECDH & Coordinate Conversions: Details the necessity of Edwards-to-Montgomery coordinate conversions for computing X25519 shared secrets, referencing RFC 7748.
• Domain Separation: Catalogs all wraith: prefixes (spending:, viewing:, scalar:, tag:) and their exact collision-prevention boundaries.
• View Tag Optimization: Documents the 1-byte view tag derivation logic and its 99.6% false-positive filtering performance value.
• Custom Signing API: Clarifies the signWithScalar implementation for deriving signatures from a raw stealth scalar instead of a standard 32-byte seed while upholding RFC 8032.
• Meta-address Structure: Explains the st:xlm: encoding prefix, payload concatenation, and Stellar's StrKey encoding.

Visual Documentation

Includes two Mermaid SVG diagrams for at-a-glance comprehension:

1. View Tag Scanning: A sequence diagram mapping the announcement scan flow and cheap prefilter logic.
2. Key Derivation Flow: A flowchart tracing ephemeral keys, ECDH operations, and point additions to form a final Stellar address.

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[emarkees]

@truthixify Kindly review branch

[truthixify]

Architecture page content + docs.json + federation cross-link look good. The 2170-line package-lock.json shouldn't be in the PR (this repo is pnpm).

rm package-lock.json
git add package-lock.json
git commit --amend --no-edit
git push --force-with-lease

[emarkees]

@truthixify Issue ahs been fixed but there is a compiled error

[truthixify]

Lockfile gone, rebased cleanly. 98-line Stellar cryptography architecture page + federation cross-link + snippet-check script tweak. Thanks @emarkees.