feat(geschichte): add GeschichteType, JourneyItem entity, GeschichteSummary, and V72 migration
- GeschichteType enum {STORY, JOURNEY} — default STORY
- JourneyItem entity replaces geschichten_documents junction table;
position-ordered, document_id nullable (note-only items allowed),
CHECK(document_id IS NOT NULL OR note IS NOT NULL)
- GeschichteSummary interface projection for list() queries (avoids lazy-init)
- Geschichte entity gains `type` + `items` (LAZY, orphanRemoval, CascadeType.ALL)
replacing the old `documents` ManyToMany bag
- GeschichteUpdateDTO: remove documentIds (replaced by JourneyItem API)
- V72 migration: adds `type` column, creates `journey_items` table with
FK ON DELETE CASCADE (geschichte) / ON DELETE SET NULL (document),
migrates geschichten_documents ordered by meta_date, drops junction table
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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