Rebrand from MyCrib to Casera

- Update Go module from mycrib-api to casera-api
- Update all import statements across 69 Go files
- Update admin panel branding (title, sidebar, login form)
- Update email templates (subjects, bodies, signatures)
- Update PDF report generation branding
- Update Docker container names and network
- Update config defaults (database name, email sender, APNS topic)
- Update README and documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Makefile

@@ -1,9 +1,9 @@
 .PHONY: build run test clean deps lint docker-build docker-up docker-down migrate
 
 # Binary names
-API_BINARY=mycrib-api
-WORKER_BINARY=mycrib-worker
-ADMIN_BINARY=mycrib-admin
+API_BINARY=casera-api
+WORKER_BINARY=casera-worker
+ADMIN_BINARY=casera-admin
 
 # Build flags
 LDFLAGS=-ldflags "-s -w"
@@ -107,7 +107,7 @@ swagger:
 
 # Help
 help:
-	@echo "MyCrib API Go - Available targets:"
+	@echo "Casera API Go - Available targets:"
 	@echo ""
 	@echo "Build:"
 	@echo "  deps          - Install dependencies"