Break A and E technical into subdecks

DESIGN.md

@@ -494,25 +494,44 @@ output artifacts.
 ```
 anki/
   amateurfunk-technische-kenntnisse-n.apkg        (195 cards)
-  amateurfunk-technische-kenntnisse-e.apkg        (463 cards)
-  amateurfunk-technische-kenntnisse-a.apkg        (716 cards)
+  amateurfunk-technische-kenntnisse-e.apkg        (463 cards, 11 sub-decks)
+  amateurfunk-technische-kenntnisse-a.apkg        (716 cards, 11 sub-decks)
   amateurfunk-betriebliche-kenntnisse.apkg        (172 cards)
   amateurfunk-kenntnisse-von-vorschriften.apkg    (204 cards)
 ```
 
-Five `.apkg` files. Betriebliche and Vorschriften are shared across
-every candidate (class-1-only in the data per §3 axis 2) and stay as
-one deck each. Technische is fanned out per license class using a
-**strict equality split** on the question's `class` field — class-1
-questions land in the N deck only, class-2 in E only, class-3 in A
-only. The card counts therefore equal the new-at-this-class slices
-from §3, not the cumulative study pools: a candidate studying for
-class E imports Technische-N + Technische-E + Betriebliche +
-Vorschriften.
+Betriebliche and Vorschriften are shared across every candidate
+(class-1-only in the data per §3 axis 2) and stay as one deck each.
+Technische is fanned out per license class using a **strict equality
+split** on the question's `class` field — class-1 questions land in
+the N deck only, class-2 in E only, class-3 in A only. The card counts
+therefore equal the new-at-this-class slices from §3, not the
+cumulative study pools: a candidate studying for class E imports
+Technische-N + Technische-E + Betriebliche + Vorschriften.
+
+The class-E (463) and class-A (716) Technische pools are large enough
+that a single flat deck is unwieldy, so each package is built as a deck
+*tree* rather than fanned out into separate files: one `.apkg`
+containing one sub-deck per first-level catalog topic (the 11
+subsections under the Prüfungsteil, e.g. "Sender und Empfänger",
+"Antennen und Übertragungsleitungen") plus an anchoring `…::E` / `…::A`
+parent deck. Each card is filed under its topic via the `did` column;
+grouping is by the first section title below the Prüfungsteil
+(`item.path[1]`). Anki sorts the sub-decks alphabetically on import (it
+has no per-deck manual ordering), not in catalog order. N (195) is
+small enough to stay one flat deck. The split classes are listed in
+`TOPIC_SPLIT_CLASSES`. These multi-deck packages list every sub-deck in
+the `col.decks` blob (see `build_apkg_for_category` and
+`insert_collection_metadata`).
+
+Note that re-importing a reworked package does not move cards that
+already exist in a collection — Anki only files *new* cards by the
+package's decks and leaves existing cards in their current deck.
 
 The Technische deck names use Anki's `::` hierarchy separator
-(`Amateurfunk::Technische Kenntnisse::N`) so the three decks render
-as children of a shared parent in Anki's deck browser. The
+(`Amateurfunk::Technische Kenntnisse::N`, and one level deeper for E/A —
+`Amateurfunk::Technische Kenntnisse::A::Sender und Empfänger`) so the
+decks render as a nested tree in Anki's deck browser. The
 `klasse-N` / `klasse-E` / `klasse-A` tag is still emitted on every
 note — redundant within each Technische deck but useful in Betr/Vor
 for in-Anki filtering, and harmless besides.