refactor: restructure from 3-phase to 4-phase model
Separate "what to build" (Zielbild) from "how to build it" (Planning):
- Phase 1: Discovery (unchanged)
- Phase 2: Zielbild / Target Vision (new, technology-agnostic)
- Phase 3: Planning / Architecture & Technology (was Phase 2)
- Phase 4: Integration / Implementation (was Phase 3)
Rename directories: B_planning→B_target, C_integration→D_integration,
add C_planning. Move decisions-log.md to C_planning.
Update all references across commands, rules, templates, and docs.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
c766abdb2b