Add design spec for alpha-id ICD code suggestion PoC

Brainstormed design: free-text dictation (marker-segmented by
doctate) -> single prioritized top-10 ICD-10-GM list with tag
filtering. Two modes (C lexical baseline, A hybrid retrieval +
IONOS bge-m3 + Qwen3-VL-Reranker-8B), eval harness via synthetic
transcription errors, one-time cost-guarded embedding.

Licensed BfArM data dirs and local settings are gitignored.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,12 @@
+# Lizenzierte BfArM-Referenzdaten (lokal halten, siehe downloadbedingungen-2025.pdf)
+/data/
+/icd-claml/
+
+# Rust-Build
+/target/
+
+# Embedding-/Index-Cache (regenerierbar, ggf. groß; siehe Spec §4)
+/index/
+
+# Lokale, persönliche Claude-Code-Overrides (nicht teamweit)
+/.claude/settings.local.json