docs(normalizer): README + seed overrides

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tools/import-normalizer/README.md

@@ -0,0 +1,38 @@
+# Import Normalizer
+
+Transforms the raw family-archive spreadsheets in `../../import/` into a clean canonical
+dataset (`out/`) plus review reports (`review/`). See the spec:
+`../../docs/import-migration/02-normalization-spec.md`.
+
+## Setup
+Requires **Python 3.12** (uses `StrEnum`).
+```bash
+python3 -m venv .venv && .venv/bin/pip install -r requirements.txt
+```
+
+## Run
+```bash
+.venv/bin/python normalize.py
+```
+Outputs:
+- `out/canonical-documents.xlsx`, `out/canonical-persons.xlsx`
+- `review/*.csv` (residue to fix), `review/summary.txt` (grouped run stats incl. unknown-date rate)
+
+## Iteration loop
+1. **Run.** Read `review/summary.txt` for the health snapshot.
+2. **Fix the residue** by editing the version-controlled overrides files, then re-run. Repeat.
+
+| Review file | What to do |
+| --- | --- |
+| `unparsed-dates.csv` | For each `raw` (sorted by frequency), fill `suggested_iso` + `suggested_precision`, then paste `raw,suggested_iso,suggested_precision` into `overrides/dates.csv` (header `raw,iso,precision`). |
+| `unmatched-names.csv` | If `suggested_id` is right, copy `raw,suggested_id` into `overrides/names.csv`; else look up the correct id in `out/canonical-persons.xlsx` (the `person_id` column). |
+| `ambiguous-receivers.csv` | A space-joined pair we refused to auto-split (e.g. `Ella Anita`). Decide and add a names override if it is really two people. |
+| `index-file-mismatch.csv` | The `Datei` path disagrees with the index-derived filename — reconcile when the PDFs arrive. |
+| `duplicate-index.csv`, `blank-index-rows.csv`, `skipped-x-suffix.csv` | Inspect; fix in the source spreadsheet if needed. |
+
+**Valid `person_id` values** all come from the `person_id` column of `out/canonical-persons.xlsx`.
+
+## Tests
+```bash
+.venv/bin/python -m pytest tests/test_dates.py -v   # run files individually (never the whole suite at once)
+```