fix: prevent split payment failures from blocking remaining targets

[hexdaemon]

Summary

• Wrap per-target processing in try/except so one failed target logs an error and continues instead of aborting all remaining splits (critical: this was silently stopping payments)
• Make LNURL detection case-insensitive — lowercase lnurl1... (the canonical bech32 form) was rejected at the API or misrouted as a wallet ID at payment time
• Add minimum amount guard — sub-1-sat split amounts produced 0-amount invoices that crashed create_invoice, which then triggered the above cascading failure
• Add post-fee-reserve minimum for LNURL targets — after subtracting fee_reserve, the amount could go negative/zero
• Re-raise HTTPException before generic handler in api_targets_set — validation errors (invalid wallet, self-split, bad percent, over-100%) were being swallowed by a blanket except Exception and returned as a generic 500 "Cannot set targets"
• Fix migration m003 — row["tag"] read from a table that has no tag column, causing KeyError when migrating existing data
• Fix done_callback — replaced lambda fut: logger.success(fut.result()) which logged success(None) on failure with a proper helper
• Fix frontend isTargetComplete — removed reference to deleted tag field that made dirty-checking always pass

Test plan

• Configure split targets with a valid internal wallet and verify payments split correctly
• Configure an LNURL target (lowercase lnurl1...) and verify it is accepted and paid
• Send a very small payment (e.g. 1 sat with a 50% split) and verify the sub-1-sat target is skipped with a log warning rather than crashing
• Configure one target as an invalid/deleted wallet and a second as valid — verify the second target still receives payment
• Attempt to save targets with invalid wallet, self-split, or >100% total and verify the API returns a descriptive 400 error (not a 500)
• Verify the frontend dirty indicator works correctly when adding/removing targets

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