feat(infer): messages starting with "other:" are not monthly fees

When the bank message starts with "other:" (case-insensitive),
inference does not look for a month, neither in the text nor from the
payment date. The trimmed message is written to Purpose, so reconcile
books the payment as an "other" transaction for the person instead of
a monthly fee. Messages containing "other:" elsewhere are unchanged.

- matching.IsOtherPurpose / is_other_purpose shared by inference and
  reconcile
- reconcile applies the rule to rows not yet processed by inference
- no person found: Purpose is still written, row shows as unmatched
- implemented in Go and legacy Python; four new parity fixtures

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -164,6 +164,8 @@ Both implementations check the Drive API `modifiedTime` and serve a cached JSON
 
 `Person` and `Purpose` are written by the inference step (`fuj infer` / `infer_payments.py`) and can be manually corrected. `manual fix` column presence disables re-inference for that row. Multiple people or months are comma-separated in Person/Purpose.
 
+**Non-fee payments ("other")**: a Purpose that starts with `other:` (case-insensitive) is attached to the person's "other transactions" and is not counted against any month. Inference produces this by itself when the bank message starts with `other:`: it copies the trimmed message into Purpose and does not look for a month (neither in the text nor from the date). A message that only contains `other:` later in the text is inferred the normal way. The shared check is `matching.IsOtherPurpose` / `is_other_purpose`.
+
 ### QR codes
 
 `/qr?account=…&amount=…&message=…` generates a Czech QR Platba PNG (SPD format).