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>

go.mod

@@ -7,4 +7,20 @@ require (
 	github.com/gorilla/websocket v1.5.3
 )
 
-require github.com/mattn/go-sqlite3 v1.14.32
+require modernc.org/sqlite v1.34.4
+
+require (
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/hashicorp/golang-lru/v2 v2.0.7 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/ncruces/go-strftime v0.1.9 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	golang.org/x/sys v0.22.0 // indirect
+	modernc.org/gc/v3 v3.0.0-20240107210532-573471604cb6 // indirect
+	modernc.org/libc v1.55.3 // indirect
+	modernc.org/mathutil v1.6.0 // indirect
+	modernc.org/memory v1.8.0 // indirect
+	modernc.org/strutil v1.2.0 // indirect
+	modernc.org/token v1.1.0 // indirect
+)