refactor(db): use regex instead of fixed substr in repairSequences

[khaira777]

Context

In PR #28, repairSequences() was added to main/db.ts to rebuild sequence counters from existing order/bill data on startup. It works correctly but parses order/bill numbers using fixed substr positions:

substr(order_number, 5, 8)   // date
substr(order_number, 14)      // sequence number

Problem

This is fragile — if the numbering format ever changes (e.g. longer prefixes, different separators), the extraction silently returns wrong values.

Proposed Fix

Replace substr with a regex:

const match = row.order_number.match(/^ORD-(\d{8})-(\d+)$/);
if (match) { /* match[1] = date, match[2] = sequence */ }

Priority

Low — the current format (ORD-YYYYMMDD-NNNN / INV-YYYYMMDD-NNNN) is stable and the function runs with try/catch, so no risk today. Just a robustness improvement for the future.

[khaira777]

#28 (comment)