feat(KB-336): rename data directory from .kb to .fusion

- Rename data directory from .kb to .fusion across core, CLI, dashboard, and engine
- Update all path references in source files, tests, and CLI output
- Remove deprecated central-core infrastructure (central-core, central-db, central-integration)
- Remove obsolete test files (PlanningModeModal.test.tsx, ScheduleForm.test.tsx)
- Add changeset for the directory rename breaking change

packages/dashboard/app/components/SettingsModal.tsx

@@ -14,7 +14,7 @@ import { applyPresetToSelection, generatePresetId, validatePresetId } from "../u
  * Each section groups related settings fields under a sidebar nav item.
  * Sections have a `scope` to indicate where their settings are stored:
  *   - "global": User-level settings stored in ~/.pi/kb/settings.json (shared across projects)
- *   - "project": Project-specific settings stored in .kb/config.json
+ *   - "project": Project-specific settings stored in .fusion/config.json
  *   - undefined: Section operates independently of settings storage (e.g. authentication)
  *
  * To add a new section:
@@ -1256,8 +1256,8 @@ export function SettingsModal({
               <input
                 id="autoBackupDir"
                 type="text"
-                placeholder=".kb/backups"
-                value={form.autoBackupDir || ".kb/backups"}
+                placeholder=".fusion/backups"
+                value={form.autoBackupDir || ".fusion/backups"}
                 onChange={(e) =>
                   setForm((f) => ({ ...f, autoBackupDir: e.target.value }))
                 }