#108 Feature: Implement Lightning Address

[andycreed0x]

Purpose

Implements Lightning Address support for JAN3/AQUA accounts. Closes #108 Feature: Implement Lightning Address.

Each AQUA user has a Lightning Address (ln_username@<domain>) assigned by the backend. This PR exposes the full LN-address lifecycle as MCP tools and CLI commands: check username availability, purchase a username with an on-chain L-BTC payment, enable/disable delivery, and keep the unused Liquid address pool healthy so the backend can deliver inbound Lightning payments.

Description

The backend delivers inbound Lightning payments to a rotating batch of off-chain Liquid receive addresses registered by the client. Because these addresses are handed out before any on-chain activity, lwk's next-unused tip can't track them — WalletData now persists a monotonically-increasing next_address_index counter so two flows never share an address. The pool self-heals: jan3_user_info and jan3_enable_lightning_address both call ensure_ln_pool (best-effort, never failing the primary operation).

Main Changes

• ✨ Added jan3_user_info — account profile + auto pool top-up when LN-address is active
• ✨ Added jan3_enable_lightning_address — opt in/out; on enable immediately registers a Liquid address batch
• ✨ Added jan3_ln_check_username — availability check before paying L-BTC
• ✨ Added jan3_purchase_ln_username — on-chain L-BTC payment to buy/update the LN username; computes txid locally from the raw tx since the API omits it
• ✨ Added register_ln_addresses / ensure_ln_pool / _auto_ensure_ln_pool internal manager methods (jan3_accounts.py) for pool lifecycle; not exposed as MCP tools
• ✨ Added Jan3AccountsClient API methods: get_user, ln_address_toggle, ln_username_available, register_addresses, create_ln_username_payment_request, submit_raw_tx
• 🏗️ Added WalletData.next_address_index (storage.py) with migration from legacy ln_addr_next_index key; advances via WalletManager.reserve_addresses
• ✨ Added CLI commands: aqua jan3 user-info, enable-lightning-address, ln-check-username, purchase-ln-username (cli/jan3.py)
• 🔧 Updated features.py CLI→MCP mappings for new commands
• ✨ Added next_step hint to jan3_verify / jan3_login_complete results to cue agents to offer LN-address opt-in post-login
• ✅ Added tests in test_jan3_accounts.py, test_storage.py, test_tools.py, test_wallet.py (~600 lines)

Checklist

• No hardcoded values (they should go in constants.py, .env, or our database)
• Added/updated tests (if necessary)
• Added/updated relevant documentation (if necessary)