fix: Pin modernc.org/sqlite to 1.38.2 to avoid FK regression (bd-101, GH#144)

SQLite 1.39.1 (wrapping SQLite 3.50.4) introduced a FOREIGN KEY constraint
failure when closing issues via MCP/daemon mode. CLI mode works fine.

Pinning to 1.38.2 until we can investigate and resolve the root cause.

Tracked in bd-103 for future upgrade.

Amp-Thread-ID: https://ampcode.com/threads/T-1ccb2c50-5d52-4bde-b15c-3f052854689a
Co-authored-by: Amp <amp@ampcode.com>

go.mod

@@ -9,6 +9,7 @@ require (
 	github.com/fatih/color v1.18.0
 	github.com/google/uuid v1.6.0
 	github.com/spf13/cobra v1.10.1
+	github.com/spf13/viper v1.21.0
 	golang.org/x/mod v0.29.0
 	golang.org/x/sys v0.36.0
 	gopkg.in/natefinch/lumberjack.v2 v2.2.1
@@ -31,7 +32,6 @@ require (
 	github.com/spf13/afero v1.15.0 // indirect
 	github.com/spf13/cast v1.10.0 // indirect
 	github.com/spf13/pflag v1.0.10 // indirect
-	github.com/spf13/viper v1.21.0 // indirect
 	github.com/subosito/gotenv v1.6.0 // indirect
 	github.com/tidwall/gjson v1.18.0 // indirect
 	github.com/tidwall/match v1.1.1 // indirect