Show years in chit installment dates

Summary

Updated the chit detail installment table to include the year in every displayed payment date while preserving the existing inline date-editing behavior. Added a regression test covering installments across two years and confirming that editing still receives the original ISO date. Committed and pushed the change to origin/main as 7622726 (fix: include year in chit installment dates). Verification passed for the focused Vitest suite (20 tests across chit detail, chit list, and date helpers), TypeScript project checks, the Impeccable detector (no findings), and git diff --check.

Decisions

• Kept the shared prettyDate formatter unchanged and appended the ISO year only in chit installment rows so date formatting elsewhere in the app remains unaffected.

Learnings

• The shared prettyDate helper intentionally emits only day and abbreviated month, which caused installment dates from different years to be ambiguous.