Materialfluss: Ein-/Ausgabestationen im Chain-Graph zeichnen

BTMT Beladung/Entladung bzw. die generischen Eingang/Ausgang-Symbole waren
bislang von --chain-graph ausgenommen und wurden als Kantenziel einfach
uebersprungen. Die Anlage laeuft als Kreislauf, diese Stationen sind ihre
einzigen Materialquellen/-senken und gehoeren als eigene Knoten in jeden
Graphtyp (coarsebox/compound/subgraph).

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

doc/Python_Scripts.md

@@ -244,7 +244,7 @@ See `doc/track.md` for the fuller derivation notes.
 | `--show-bbs` | — | off | Also write `<name>_bbs.svg`: a plain 2-D top-down view of every CSV row (not just flow nodes — Separator/Scanner/Ein-/Ausschleuselement too), one axis-aligned rectangle per row from the `Position` column (its center, X/Y) and the `Boundingbox` column (its width/depth, X/Y — the Z extent is ignored), with the row's `Bezeichnung` centered in it. A Kreisel is the one exception: instead of one rectangle for the whole ring, it's split into its two Bahn L/R halves (`_kreisel_lane_rects()` — short axis divided in half, `Zuordnung`-majority-vote decides which half is L vs R), each drawn and labelled separately; its K1–K4 points (with `--show-kx`) still belong to the Kreisel as a whole and are drawn once, not per half. No rotation, no Graphviz — hand-built SVG; the `viewBox` stays in plant millimetres (Y flipped so plant "up" renders as screen "up") but the printed page size is scaled to DIN A3 (landscape or portrait, whichever matches the layout's aspect ratio) instead of the plant's real-world extent. Larger objects are drawn first so small ones (Separator, Scanner, …) stay visible on top. |
 | `--show-kx` | — | off | Only valid together with `--show-bbs` (else exit 1). Additionally draw each object's connection coordinate systems K1–K4 into the `_bbs.svg`: the K1–K4 columns are 12-char base64 strings (three 24-bit fixed-point values `x,y,z`, factor 10, `csv:trans-encode` in `dxfmakros/Lisp/export.lsp`) decoded to a plant-mm X/Y. Each present K-point is drawn as a small red cross (two lines) with a small `K1`…`K4` label, and consecutive points are joined `K1→K2→K3→K4` by a blue line. Empty K columns are skipped, so an object with only K1/K2 gets two crosses and one link. |
 | `--track` | — | off | Additionally write the finer Separator/Ausschleus/Einschleus/Weiche graph described above (`<name>_track.dot`, and `<name>_track.svg` with `--tosvg`). Does not change the normal `_material_flow.*` output. See `doc/track.md`. |
-| `--chain-graph` | — | off | Write a "chain-/Lageplan" of the **grobe Objekte** (big items): every Kreisel split into its Bahn L/R halves (`_kreisel_lane_rects()`, same split as `--show-bbs`) and every Strecke/Gefällestrecke ("VF"/"GF"), connected by the already-resolved top-level `graph.edges` (material flow, Kreisel-Umlauf, unresolved). Still no BTMT Ein-/Ausgang — an edge touching a node that isn't drawn (e.g. a station) is simply skipped. Rendering method and output file are chosen by `--graphtype`. |
+| `--chain-graph` | — | off | Write a "chain-/Lageplan" of the **grobe Objekte** (big items): every Kreisel split into its Bahn L/R halves (`_kreisel_lane_rects()`, same split as `--show-bbs`), every Strecke/Gefällestrecke ("VF"/"GF"), and every Ein-/Ausgabestation (BTMT `Beladung`/`Entladung`, or the generic `Eingang`/`Ausgang` symbol where no BTMT station absorbed it — see `_merge_station_symbols()`) — the plant runs as a closed loop, so these stations are its only material sources/sinks and are drawn like any other node, not skipped. Connected by the already-resolved top-level `graph.edges` (material flow, Kreisel-Umlauf, unresolved). Rendering method and output file are chosen by `--graphtype`. |
 | `--graphtype` | `coarsebox`\|`compound`\|`subgraph` | `coarsebox` | Only valid together with `--chain-graph` (else exit 1). `coarsebox`: containers only (as above), to real scale, hand-built `<name>_chain.svg`, no Graphviz — the original behaviour. `compound`: the same to-scale picture, **plus** each container's Anbauteile (Separator, Scanner, Ausschleus-/Einschleuselement, Weiche) drawn nested inside it at their real position (`_container_children()` reads them off `Element.track_ids`, the same source `build_track_graph()`/`--track` uses — not a re-derivation from `Nachbarn` like the old `data/gen_chain_svg.py` prototype), linked by the already-resolved `TrackGraph.edges`; still `<name>_chain.svg`, no Graphviz. `subgraph`: the same containment expressed as **nested Graphviz clusters** (`subgraph cluster_*` — one per Kreisel, nested one per Bahn L/R, plus one per Strecke/Gefällestrecke, each containing its Anbauteile as child nodes) — schematic (`dot` auto-layout), **not** to scale; writes `<name>_chain.dot` always, and `<name>_chain.svg` additionally with `--tosvg` (needs Graphviz `dot`, unlike the other two graph types). |
 
 **Output** (in `%SKEL_RESULTS%`): `<name>_material_flow.dot` (always, with `pos`