docs: document the account and asset-wallet cutover

[darioAnongba]

Summary

• document the breaking account-owned, asset-scoped wallet API and dashboard wallet selection flow
• describe the final production backfill assumptions: OAuth2/Auth0 identities, native BTC mainnet, no testnet data, no legacy API-key backfill, and no migration-only environment variables
• document account profile/preferences, admin account CRUD and permission grants, wallet-scoped payments/invoices/addresses, and active-network Lightning Address routing
• explain that account responses embed lightweight wallets with asset/balance data while wallet-by-ID endpoints hydrate child resources
• document the multi-network wallet catalog and operation-boundary provider/network validation contract
• distinguish the Account Directory/Details from the Wallet Directory/Details and their cross-links
• clarify that /v1/me is ownership-scoped while permission arrays add administrative API access
• clarify that admin-created accounts are identity-less, cannot sign in, and do not acquire an identity through the current authentication flows
• repair related documentation links

Validation

• yarn fm:check
• yarn lint
• yarn typecheck
• yarn build

Implementation Stack

• feat: add account administration API swissknife#331
• feat: add dashboard account wallet context swissknife#332
• refactor: align user modules with accounts swissknife#333
• test: complete account and wallet integration coverage swissknife#334
• feat: expose account wallet aggregates swissknife#336
• docs: reconcile identity migration and multi-network wallets swissknife#340 (includes the multi-network ADR update formerly split into #341)
• feat: consolidate account and wallet administration swissknife#342

Related: bitcoin-numeraire/swissknife#297