chore: strip remaining pre-fork version references

Second pass — removes chat-switchboard version numbers from config
field docs, section headers, file headers, and test comments. These
were pre-fork version tags that don't apply to switchboard-core.

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

server/handlers/notifications.go

@@ -175,7 +175,7 @@ func (h *NotificationHandler) Delete(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"ok": true})
 }
 
-// ── Notification Preferences (v0.20.0 Phase 3) ──
+// ── Notification Preferences ──
 
 // GET /api/v1/notifications/preferences
 func (h *NotificationHandler) ListPreferences(c *gin.Context) {
@@ -282,7 +282,7 @@ func (h *NotificationHandler) DeletePreference(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"ok": true})
 }
 
-// ── Admin Broadcast (v0.28.6) ───────────────
+// ── Admin Broadcast ───────────────
 
 // POST /api/v1/admin/notifications/broadcast
 // Admin-only: sends a system.announcement notification to all active users.