German date display + optional street address for precise geocoding

- Date pickers (entry form + edit dialog) now display TT.MM.JJJJ instead of
  ISO (DATE_DISPLAY_FORMAT). Storage stays YYYY-MM-DD; parse_date() already
  accepted both formats, so existing data and the self-updater are unaffected.
- New optional "Straße" field (street + house number) in the entry form and
  edit dialog, backed by a new `street` CSV column. geocode_city() and
  GeocoderWorker.enqueue() gained a street parameter: when set, a full-address
  query is tried first for a much more precise map point, falling back
  automatically to the existing city/PLZ search if it doesn't resolve.
- Tab 2 and the entry queue show a Straße column; Tab 2 search now also
  matches on street.
- Fix: pandas turns a blank CSV cell into NaN even for a dtype=str column, so
  every existing (blank-street) row would have shown literal "nan" in Tab 2.
  DataStore._load now does street.fillna("") after every read.

Verified with a non-GUI test suite (date parsing, query construction, CSV
round-trip incl. the NaN case) and a full GUI build/drive test on Python
3.12/Tk 9. Docs updated (changelog, overview, architecture, data-model,
dev-notes, improvements).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/overview.md

@@ -16,14 +16,16 @@ Workflow: build up a **queue** of entries, let them geocode in the background,
 then save the whole batch at once.
 
 1. **Entry form** – date (a **calendar picker**, `ttkbootstrap.DateEntry`,
-   pre-filled with today; typed input is accepted in `JJJJ-MM-TT` or
-   `TT.MM.JJJJ` and **validated** – an invalid date is rejected with a dialog),
-   city (autocomplete combobox), postal code (optional). Pressing `Return` in any
-   field, or the **+ Hinzufügen** button, adds the row to the queue.
-   The PLZ field only accepts digits.
-2. **Queue table** – shows date, city, PLZ, and a live coordinate column that
-   updates from `⏳ wird gesucht…` to either `lat / lon` or `⚠ nicht gefunden`
-   as the background geocoder works through the queue.
+   pre-filled with today and **displayed as `TT.MM.JJJJ`**, e.g. `12.09.2026`;
+   typed input also accepts `JJJJ-MM-TT` and is **validated** – an invalid date
+   is rejected with a dialog), city (autocomplete combobox), postal code
+   (optional, digits only), and **Straße** (street + house number, optional,
+   second row of the form) — see [Geocoding behaviour](#geocoding-behaviour) for
+   why it's worth filling in. Pressing `Return` in any field, or the
+   **+ Hinzufügen** button, adds the row to the queue.
+2. **Queue table** – shows date, city, PLZ, street, and a live coordinate column
+   that updates from `⏳ wird gesucht…` to either `lat / lon` or
+   `⚠ nicht gefunden` as the background geocoder works through the queue.
    - Select a row and press <kbd>Delete</kbd>, use the **"Auswahl entfernen"**
      button, or click the `✕` cell.
    - Right-click a row for *Entfernen* / *Koordinaten erneut suchen*.
@@ -38,10 +40,12 @@ then save the whole batch at once.
 
 A table view of everything in `orte.csv`.
 
-- **Columns:** Datum, Ort, PLZ, and **Karte** – a status column showing `✓` when
-  the row has coordinates or a red `fehlt` when it doesn't (the whole row is red
-  too). The raw lat/lon numbers live in the edit dialog, not this table.
-- **Search box** – live filter across date, city, and PLZ (substring match).
+- **Columns:** Datum, Ort, PLZ, Straße, and **Karte** – a status column showing
+  `✓` when the row has coordinates or a red `fehlt` when it doesn't (the whole
+  row is red too). The raw lat/lon numbers live in the edit dialog, not this
+  table.
+- **Search box** – live filter across date, city, PLZ, **and street**
+  (substring match).
 - **Sortable columns** – click a header to sort; clicking again reverses. The
   active column shows a ▲/▼ arrow. Default sort is by date, newest first.
   Sorting by **Karte** groups the rows without coordinates together.
@@ -49,10 +53,11 @@ A table view of everything in `orte.csv`.
   coordinates yet. The hint line always shows the total count, plus how many are
   missing coordinates.
 - **Edit** – double-click a row (or *Bearbeiten*) opens a modal dialog to change
-  date (calendar picker, validated) / city / PLZ. Two ways to fix coordinates:
-  a "Koordinaten automatisch neu suchen" toggle re-runs geocoding after saving,
-  or the **Breitengrad / Längengrad** fields let you type them in by hand
-  (both empty = no map marker).
+  date (calendar picker, `TT.MM.JJJJ`, validated) / city / PLZ / **Straße**. Two
+  ways to fix coordinates: a "Koordinaten automatisch neu suchen" toggle re-runs
+  geocoding after saving (now using the street if one is set), or the
+  **Breitengrad / Längengrad** fields let you type them in by hand (both empty =
+  no map marker).
 - **Right-click → Koordinaten suchen** – runs geocoding for that one row
   (handy for rows that failed the first time).
 - **Delete** – *Löschen* removes the selected row(s) after a confirmation
@@ -87,13 +92,22 @@ Generated by `generate_map()`:
 
 ## Geocoding behaviour
 
-`geocode_city(city, postal_code)` tries a series of queries in order and returns
-the first hit:
+`geocode_city(city, postal_code, street="")` tries a series of queries in order
+and returns the **first hit**:
 
-1. `"<PLZ> <city>, Germany"` (only if a PLZ was given)
-2. `"<city>, Baden-Württemberg, Germany"`
-3. `"<city>, Hessen, Germany"`
-4. `"<city>, Germany"`
+1. `"<street>, <PLZ> <city>, Germany"` — only if a **street** was given (with
+   PLZ if there is one, without it if not). This is what the optional Straße
+   field is for: a full address geocodes far more precisely than a city name
+   alone (a point in the right town vs. the right building).
+2. `"<PLZ> <city>, Germany"` (only if a PLZ was given)
+3. `"<city>, Baden-Württemberg, Germany"`
+4. `"<city>, Hessen, Germany"`
+5. `"<city>, Germany"`
+
+If the street-level query (1) doesn't match anything in Nominatim (typo, house
+number Nominatim doesn't know, etc.), it **falls back automatically** to the
+same city/PLZ-level searches used when no street is given — a bad street never
+makes geocoding *worse* than before, only better when it resolves.
 
 The regional bias is the `GEOCODE_REGIONS` constant (`Baden-Württemberg`,
 `Hessen`) near the top of `app.py`. Results are rounded to five decimal places.