Two small money-parsing faults in ai-bookkeeper: half cents and negative zero

ai-bookkeeper keeps money in integer cents, so the one place a float can leak in is parseCents. A probe with 20 odd strings found two faults.

• 1.005 came out as 100 cents. In floating point 1.005 * 100 is 100.49999999999999, so rounding that product drops the half cent. It now rounds the decimal value (101); 2.675 gives 268 instead of 267.
• -0.001 came out as -0 cents. It prints as 0 but fails Object.is(x, 0) and strict deep-equal checks. It is now plain 0.

Both are pinned in parsecents-rounding.test.mjs. The full suite (1,256 tests) passes. Half-cent amounts are rare in bank exports, so this is hygiene, not a user-visible fix; the probe used my own strings, not a real export.