feat: top up an identity from one of the wallet's own Platform addresses

[LexxXell]

Draft. Sits on #171 (registration from a Platform address), which in turn sits on #168. Until those merge this diff carries their commits and CI fails the same way (calculateMinRequiredFee needs #167). Merge order: #167 / #169 → #168 → #171 → this one.

Changes

Top-up of an existing identity paid from one of the wallet's own Platform addresses — the counterpart of the registration in #171, on the same journal.

• IdentityFundingService.quotePlatform now signs either transition: identity create for a registration, IdentityTopUpFromAddresses for a top-up of the identity the payload names.
• TOP_UP_IDENTITY_FROM_PLATFORM_ADDRESS confirms such a quote by broadcasting the stored bytes and waiting for Platform to credit the identity. No identity is created, so nothing is resolved or saved afterwards.

Everything else is inherited: the address is the one asked for or the largest covering the amount, the nonce is signed into the bytes so a retry sends exactly them, and while the operation is pending the wallet's other Platform spends are refused.

Backend only — no UI changes.

Testing

• tsc --noEmit, ts-standard
• test/api/private/identities/identityFunding.spec.ts — four new cases: a top-up quote stores signed bytes and reserves no identity index; confirming sends exactly those bytes, makes no identity lookup and never touches Core; a top-up without a valid identifier is refused by validatePayload; a pending top-up cannot be confirmed through the registration handler.
• jest: 44 suites, 19 cases in the funding spec; the only failures are the network-dependent specs that flake on develop too and pass on a re-run.

[LexxXell]

Superseded by #177. The funding journal chain is parked on the archive/identityFundingJournal branch.