Add JSON import/export for full encounter state

Export and import encounter, undo/redo history, and player characters
as a downloadable .json file. Export/import actions are in the action
bar overflow menu. Import validates using existing rehydration functions
and shows a confirmation dialog when replacing a non-empty encounter.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -115,6 +115,7 @@ Speckit manages **what** to build (specs as living documents). RPI manages **how
 - `specs/004-bestiary/` — search index, stat blocks, source management, panel UX
 - `specs/005-player-characters/` — persistent player character templates (CRUD), search & add to encounters, color/icon visual distinction, `PlayerCharacterStore` port
 - `specs/006-undo-redo/` — undo/redo for encounter state mutations
+- `specs/007-json-import-export/` — JSON import/export for full encounter state (encounter, undo/redo, player characters)
 
 ## Constitution (key principles)
 
@@ -126,3 +127,10 @@ The constitution (`.specify/memory/constitution.md`) governs all feature work:
 4. **MVP Baseline** — Say "MVP baseline does not include X", never permanent bans.
 5. **Spec-driven features** — Features are described in living specs; evolve existing specs via `/integrate-issue`, create new ones via `/speckit.specify`. Bug fixes and tooling changes do not require specs.
 
+
+## Active Technologies
+- TypeScript 5.8 (strict mode, `verbatimModuleSyntax`) + React 19, Vite 6, Tailwind CSS v4, Lucide Reac (007-json-import-export)
+- localStorage (encounter, undo/redo, player characters) (007-json-import-export)
+
+## Recent Changes
+- 007-json-import-export: Added TypeScript 5.8 (strict mode, `verbatimModuleSyntax`) + React 19, Vite 6, Tailwind CSS v4, Lucide Reac