feat: Eliminate CGO dependency by switching to pure Go SQLite

Replaced github.com/mattn/go-sqlite3 (CGO-based) with modernc.org/sqlite
(pure Go implementation) to enable CGO-free builds while maintaining
full SQLite functionality.

Benefits:
- ✅ Cross-compilation without C compiler requirements
- ✅ Simplified build environment (no CGO_ENABLED=1)
- ✅ Reduced deployment dependencies
- ✅ Easier container builds and static linking
- ✅ Full SQLite compatibility maintained

Changes:
- Updated go.mod to use modernc.org/sqlite v1.34.4
- Updated database import to use pure Go SQLite driver
- Removed CGO_ENABLED=1 from all Makefile build targets
- Verified all binaries (skyview, beast-dump, skyview-data) build successfully

The modernc.org/sqlite package is a cgo-free port of SQLite that transpiles
the original C code to Go, providing identical functionality without CGO.

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

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

Makefile

@@ -9,19 +9,19 @@ LDFLAGS=-w -s -X main.version=$(VERSION)
 build:
 	@echo "Building skyview..."
 	@mkdir -p $(BUILD_DIR)
-	CGO_ENABLED=1 go build -ldflags="$(LDFLAGS)" -o $(BUILD_DIR)/skyview ./cmd/skyview
+	go build -ldflags="$(LDFLAGS)" -o $(BUILD_DIR)/skyview ./cmd/skyview
 
 # Build beast-dump utility binary
 build-beast-dump:
 	@echo "Building beast-dump..."
 	@mkdir -p $(BUILD_DIR)
-	CGO_ENABLED=1 go build -ldflags="$(LDFLAGS)" -o $(BUILD_DIR)/beast-dump ./cmd/beast-dump
+	go build -ldflags="$(LDFLAGS)" -o $(BUILD_DIR)/beast-dump ./cmd/beast-dump
 
 # Build skyview-data database management binary
 build-skyview-data:
 	@echo "Building skyview-data..."
 	@mkdir -p $(BUILD_DIR)
-	CGO_ENABLED=1 go build -ldflags="$(LDFLAGS)" -o $(BUILD_DIR)/skyview-data ./cmd/skyview-data
+	go build -ldflags="$(LDFLAGS)" -o $(BUILD_DIR)/skyview-data ./cmd/skyview-data
 
 # Build all binaries
 build-all: build build-beast-dump build-skyview-data