fix(pii): remove real member names tied to payments

- Scrub three parity fixtures that still held raw bank messages
- Use fictional names in the junior regression test, its changelog
  entry and its plan file
- State the rule in CLAUDE.md: a real name as a bare test input is
  fine; a real name next to payment details, or any junior or parent
  name, is not
- Tick T4 in the cleanup task list

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

go/tests/fixtures/pure/parse_month_references/real_filip_prosinec_leden_unor.json

@@ -3,7 +3,7 @@
   "func": "scripts.czech_utils.parse_month_references",
   "captured_at": "2026-05-06",
   "input": {
-    "text": "Filip Halamka - prosinec, leden, unor",
+    "text": "Member_607b748d - prosinec, leden, unor",
     "default_year": 2026
   },
   "output": {

go/tests/fixtures/pure/parse_month_references/real_jachym_numeric_multi.json

@@ -3,7 +3,7 @@
   "func": "scripts.czech_utils.parse_month_references",
   "captured_at": "2026-05-06",
   "input": {
-    "text": "Jáchym Kubík: 01/2026+03/2026+04/2026",
+    "text": "Member_71343342: 01/2026+03/2026+04/2026",
     "default_year": 2026
   },
   "output": {

go/tests/fixtures/pure/parse_month_references/real_martin_prosinec_leden.json

@@ -3,7 +3,7 @@
   "func": "scripts.czech_utils.parse_month_references",
   "captured_at": "2026-05-06",
   "input": {
-    "text": "Martin Bolvansky Pausal Prosinec Leden",
+    "text": "Member_51a8ec2d Pausal Prosinec Leden",
     "default_year": 2026
   },
   "output": {