feat: Phase 3 campaign management

Campaign CRUD API with cascading delete across all campaign-scoped
tables, a systems endpoint to seed the create-campaign form, active
campaign state wired to the sidebar chaos factor, and a campaign
management view for creating/switching/deleting campaigns.

CLAUDE.md

@@ -73,7 +73,8 @@ mythic-oracle/
 │       ├── threads.js
 │       ├── npcs.js
 │       ├── notes.js
-│       └── tables.js
+│       ├── tables.js
+│       └── systems.js
 ├── public/
 │   ├── index.html         # Shell only — sidebar + view containers
 │   ├── css/
@@ -89,7 +90,8 @@ mythic-oracle/
 │       ├── npcs.js
 │       ├── notes.js
 │       ├── character.js
-│       └── tables.js
+│       ├── tables.js
+│       └── campaigns.js   # Campaign management view UI
 ├── data/
 │   ├── tables/            # Static JSON tables — version controlled
 │   └── mythic-oracle.db   # SQLite database — gitignored