Paginate the unspent-coin read: control.wallet.coins and dign wallet coins

[MichaelTaylor3d]

Task

Paginate the unspent-coin read: control.wallet.coins and the dign wallet coins CLI that fronts it.

Parent epic: https://github.com/DIG-Network/dig_ecosystem/issues/3170

User directive, verbatim: "the dig-node cli also needs a command in its wallet to list available
coins, paginated"

What already exists — do NOT rebuild it

• control.wallet.coins — shipped, per-address, unspent-only (crates/dig-node-service/src/control.rs:148)
• dign wallet coins <ADDRESS> --asset xch|dig [--json] — shipped, unpaginated
• The persisted coins table with idx_coins_unspent … WHERE spent_height IS NULL, and
  WalletDb::unspent_coins(asset_id) (crates/dig-wallet/src/sage/db.rs)

The gap is only pagination. An address with thousands of coins currently returns everything in one
response.

The shape — reuse the repo's own Sage-parity idiom, do not invent one

crates/dig-wallet/src/sage/rpc.rs:358-366 already implements this correctly for coinsByParent.
Match it:

• ASCENDING by coin_id — a stable total order, so a page boundary is well-defined.
• Cursor, not offset. Return the last coin_id of the page; the caller resumes from it. An offset
  re-reads a shifting table and silently skips or repeats rows when a coin is spent between pages —
  and on a money surface a skipped coin reads as missing funds.
• has_more derived from rows remaining BEYOND the page, never from whether the page filled. The
  repo's own comment says why: the two differ exactly when the count is a multiple of the page size.
• An empty page is an answer, not an error (rpc.rs:1853).
• A short page is never marked complete to salvage a partial read (rpc.rs:1859).

Note the existing query's scope, and decide deliberately

unspent_coins(asset_id) filters by asset_id only — it does not filter by puzzle_hash. Check
what the RPC layer does with that before adding a page on top: if the address filter is applied above
the query, paginating the unfiltered query and then filtering would produce short pages and a wrong
has_more. Filter and paginate at the same level, in SQL, or the two disagree.

Also

• Keep --json machine output (§6.2) and make the cursor/has_more fields part of it — a scripted
  caller must be able to page without parsing prose.
• control.wallet.coins is a published contract in dig-node-control-interface; adding optional
  paging params is additive, but the catalog must be updated in the same family (§4.1 release-first).
  State the SemVer judgement.
• Update SPEC.md (§4.2) and the CLI parity test (#426 guards drift between the RPC and the CLI).
• §2.4b: bring dig-*/chia-* deps to latest in the PR; index checks need a User-Agent header.

Acceptance

dign wallet coins <address> --asset dig pages through a real funded address, --json carries the
cursor, and the last page reports has_more: false without a spurious extra request. Evidence is a
real run (§2.6).