Port codebase from Python 2 to Python 3

Replace Python 2-only constructs throughout libs/: print statements,
ConfigParser -> configparser, sets.Set -> builtin set, string.split ->
str.split, xrange -> range, dict.has_key()/.iteritems() -> in/.items(),
old-style raise Exception, "msg" syntax, and __cmp__ -> __eq__/__lt__
via functools.total_ordering (Python 3 dropped cmp()/__cmp__, which
max()/.sort() rely on). Also cleaned up mixed tab/space indentation
that Python 3's stricter tokenizer rejects.

Fixed two latent bugs that only surfaced once end-to-end runs were
possible under Python 3's stricter error handling:
- HandleBestellung() compared G.Anzahl (a bound method) to an int
  instead of calling G.Anzahl() - silently "worked" under Python 2's
  permissive cross-type ordering, raises TypeError under Python 3.
- LeuteAllein() raised KeyError for VIP-group members, who are never
  added to the regular Gruppen container; now skips people with no
  group entry instead of crashing.

Verified end-to-end: bin/platz.sh --indir work/test1 and --indir
work/test2 (VIP group included) both run to completion and produce
correctly formatted output.

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

CLAUDE.md

@@ -10,11 +10,27 @@ sizes/neighbor relationships, and a penalty scheme. It reads an XML order/guest
 table layout, runs a small custom GA framework to search for a good seating, and writes the
 result to text/CSV output files.
 
-**This is Python 2 code** (print statements, `ConfigParser`, `sets.Set`, `UserList`,
-`string.split`, old-style `raise Exception, "msg"`, `xrange`, `dict.has_key`,
-`dict.iteritems`). It will not run under Python 3 without a 2to3-style port. 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
+**This is Python 3 code**, migrated from an original Python 2 implementation (the git
+history / old comments may still say "Python 2" — that's now stale). Notable migration
+artifacts to be aware of when touching this code:
+- `Gruppe`, `Loesung`, and `Sitzplatzverteilung` use `@functools.total_ordering` with
+  `__eq__`/`__lt__` instead of the old Python 2 `__cmp__` (Python 3 dropped `__cmp__` and
+  `cmp()` entirely; `max()`/`.sort()` need rich comparisons).
+- `sets.Set` → builtin `set`; `ConfigParser` → `configparser`; `string.split` →
+  `str.split`; `xrange` → `range`; `dict.has_key(k)` → `k in dict`; `dict.iteritems()` →
+  `dict.items()`; old-style `raise Exception, "msg"` → `raise Exception("msg")`.
+- `Strukturdaten.LeuteAllein()` was fixed to skip people with no entry in
+  `self.Gruppen.GvonPid` (e.g. VIP-group members who were never added to the regular
+  `Gruppen` container) instead of letting `GruppeVonPid` raise `KeyError` — this was a
+  latent bug that only surfaced once VIP data (`work/test2`) was actually exercised
+  end-to-end.
+- `HandleBestellung()` had a `G.Anzahl` comparison (`G.Anzahl > 0`) that used to silently
+  compare a bound method to an int under Python 2's permissive cross-type ordering;
+  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`.
 
 ## Running the program
@@ -39,8 +55,8 @@ Entry point is `libs/platz.py`, invoked via the scripts in `bin/` (each provided
   "$PLATZ_LIBS/platz.py"`. This is the actual program entry point (replaces the old
   `bin/run` / `bin/run.bat`, which hardcoded absolute paths and have been removed).
 
-`libs/platz.py` requires a command-line switch `--indir <dir>` (parsed with `optparse`,
-since this is Python 2) pointing at a directory that holds the per-run input files and
+`libs/platz.py` requires a command-line switch `--indir <dir>` (parsed with `optparse`)
+pointing at a directory that holds the per-run input files and
 receives the output files — e.g. `work/test1/`, `work/test2/`, or any new folder following
 the same layout:
 - `tische.ini` — table definitions: id, `Nummer`, `Hof` (venue/court), `Plaetze` (seats),
@@ -79,7 +95,7 @@ Domain-agnostic and reusable in principle:
 - `Farm` — owns the population (`Pool`/`PoolNeu`), and executes a `Zyklus` action-by-action
   against instances of a given solution class (passed as `Klasse` plus its constructor
   args/kwargs). `Bester()` returns the fittest (`max()`) solution found; solutions are ordered
-  via `__cmp__` on `self.value`.
+  via `__eq__`/`__lt__` (`@total_ordering`) on `self.value`.
 
 ### `Strukturdaten.py` — domain model for this specific seating problem
 - `Person`, `Gruppe` (group — a `Set` of people, splittable via `teilen()`), `Tisch` (table —