Add --tosvg switch to render seating as SVG, plus test images and docs

Sitzplatzverteilung.alsSVG() (libs/Strukturdaten.py) draws tables as
white circles and people as colored circles inside their table's
circle, colored by group membership. Table radius is derived from
the number of seats so all person-circles fit without touching; the
table-to-table grid spacing is derived from the largest table radius
so tables never overlap regardless of their Koordinaten values.

libs/platz.py gains a --tosvg switch that writes
<indir>/Sitzplatzverteilung.svg alongside the existing text/CSV
output.

The three unittest scenarios now each write their rendering to
doc/images/, and doc/docu_tests.md explains the three configurations
and what each test actually verifies (including why the "split
groups land on true neighbor tables" property only holds for a
specifically chosen seed in the circle scenario, not in general).

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

CLAUDE.md

@@ -29,9 +29,10 @@ artifacts to be aware of when touching this code:
   Python 3 raises `TypeError` for that, which is what surfaced it. Fixed to call
   `G.Anzahl()`.
 
-There is no build system, test suite, or linter configured in this repo. `requirements.txt`
-exists but is empty/commented — everything used is standard library — it's there only so
-`bin/install_py.*` has something to install into the `.venv`.
+There is no build system or linter configured in this repo. A `tests/` unittest suite
+exists (see below); `requirements.txt` is still empty/commented — everything used is
+standard library — it's there only so `bin/install_py.*` has something to install into the
+`.venv`.
 
 ## Running the program
 
@@ -81,6 +82,15 @@ GA cycle/penalty config:
 resolved as `os.path.join(indir, ...)` in `platz.py` — they are no longer configured in
 `platz.cfg`.
 
+Pass `--tosvg` to additionally write `<indir>/Sitzplatzverteilung.svg` via
+`Sitzplatzverteilung.alsSVG()` (see below).
+
+Run the test suite with `bin/run_tests.bat` / `bin/run_tests.sh` (or directly: `python -m
+unittest discover -s tests -p "test_*.py" -v`). A stray global `PYTHONPATH` entry on this
+machine points at an unrelated project that also defines a `tests` package — this shadows
+`import tests` but does not affect `unittest discover`, which is what the run_tests
+scripts use.
+
 ## Architecture
 
 Two library modules under `libs/`, imported via `PYTHONPATH=$PLATZ_LIBS`:
@@ -115,7 +125,11 @@ Domain-agnostic and reusable in principle:
   when no single table has enough free seats, recursively splitting further if needed, then
   calls `bewerten()` to score the arrangement per `Strafliste`. `mutieren()` picks the
   worst-scoring groups (`SchlechteGruppenTopX`), evicts them, and reseats them, hoping for a
-  better score. `speichern()` writes the two output files.
+  better score. `speichern()` writes the two output files. `alsSVG()` renders the layout to
+  SVG: tables as white circles sized to fit all their seats' person-circles without
+  touching, people as colored circles (color = group, via `SVGGruppenFarben`) placed evenly
+  around the inside of their table's circle. The table-to-table grid spacing is derived
+  from the largest table radius so tables never overlap regardless of their `Koordinaten`.
 - `XMLConfig` — parses `bestellung.xml` into `Personen`/`Gruppen`/VIP-group/VIP-seat-map,
   expanding each `<Person>` template by its sibling `<Anzahl>` into that many individual
   bookings, and treating any `<Gruppe>` containing a `<Tisch>` tag as a VIP group pinned to