Resume Boltz submarine swaps on 409

[andycreed0x]

Purpose

Add QR code reading capability (image → decoded string), a lightning decode CLI command to inspect BOLT11 invoices without paying them, and automatic recovery when Boltz returns a 409 "swap already exists" error by finding and resuming the existing local swap.

Main Changes

• ✨ QR decode tool (src/aqua/qr.py) — decode_qr(image_path) using zxing-cpp + Pillow; 5/5 on real phone photos including logo-overlaid QR codes
• ✨ MCP tool qr_decode — registered in tools.py + server.py; returns {"content": "<decoded_string>"}
• ✨ CLI command aqua qr decode <image_path> — new cli/qr.py group registered in commands.py
• ✨ lightning decode CLI command — aqua lightning decode --invoice lnbc... shows amount, description, expiry without paying
• ✨ MCP tool lightning_decode — same capability exposed over MCP
• 🏗️ src/aqua/bolt11.py — new module for BOLT11 protocol parsing (decode_bolt11_amount_sats, decode_bolt11_fields, bech32 tagged-field decoder); moved out of boltz.py to remove provider coupling and avoid circular import with lnurl.py
• 🐛 Boltz 409 recovery — _resume_existing_swap() in LightningManager: on duplicate invoice error, finds existing local swap, checks Boltz status, resumes if funded or re-funds if lockup address is stored
• ✨ boltz_lockup_address field added to LightningSwap dataclass — persisted at swap creation so unfunded swaps can be re-funded on recovery
• ✨ Storage.find_lightning_swap_by_invoice() — lookup swap by invoice string for 409 recovery
• 🐛 BoltzSwapAlreadyExistsError — specific exception for Boltz 409 with a dedicated HTTP status mapping; replaces generic RuntimeError
• ➕ Dependencies: zxing-cpp>=2.2, pillow>=10.0; removed opencv-python-headless (was 50MB, only needed for imread which Pillow handles)
• ✅ New test files: tests/test_qr.py (5 tests), tests/test_cli.py

⚠️ Breaking Changes

• LightningSwap.from_dict() now defaults boltz_lockup_address=None for backward compatibility with existing swap files — no migration needed

Checklist

• Added/updated tests (if necessary)
• Added/updated relevant documentation (if necessary)

[andycreed0x]

This was for solving a bug that only happend once:

• each time I wanted to pay a LN invoice, Boltz responded that invoice was was already being handled in other swap.
• it got solved deleting AA and installing it again. This PR was a in-parallel trial for solving the same issue