Add cursor-based pagination to recentLedger and wallet queries

[MrNova50]

closes #2

PR Description:

Problem
recentLedger and the wallet query in src/convex/nexis.ts truncate to the latest ~100 and ~200 entries respectively. As soon as a team actually uses the ledger, older entries silently drop out of view — undermining the auditability this project exists to provide.

Changes

• Replaced the fixed .take(100) / .take(200) caps with cursor-based pagination on both recentLedger and the wallet query, using Convex's paginationOpts pattern.
• Sort order kept as _creationTime then _id as tiebreaker — stable and gapless, so new inserts don't reshuffle already-fetched pages.
• Added a "Load more" control on the dashboard ledger that fetches and appends subsequent pages.
• Added a full-history paginated view per handle on the public proof page, using the same underlying query.
• Balance computation untouched — out of scope, tracked separately.

Testing

• Seeded 250+ ledger entries and paged forward to entry zero with no gaps or duplicates across page boundaries.
• Verified sort stability under concurrent inserts during active pagination.
• Confirmed both dashboard and public proof page load incrementally without regressing small-ledger behavior.