Add design artifacts for view event feature (007)

Spec, research, data model, API contract, implementation plan, and
task breakdown for the public event detail page.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.specify/memory/constitution.md

@@ -107,8 +107,10 @@ Accessibility is a baseline requirement, not an afterthought.
   rationale. Never rewrite or delete the original decision.
 - The visual design system in `.specify/memory/design-system.md` is authoritative. All
   frontend implementation MUST follow it.
-- Research reports go to `docs/agents/research/`, implementation plans to
-  `docs/agents/plan/`.
+- Feature specs, research, and plans live in `specs/NNN-feature-name/`
+  (spec-kit format). Cross-cutting research goes to
+  `.specify/memory/research/`, cross-cutting plans to
+  `.specify/memory/plans/`.
 - Conversation and brainstorming in German; code, comments, commits, and
   documentation in English.
 - Documentation lives in the README. No wiki, no elaborate docs site.