Rename package from shared to commons

All files now use `package commons` instead of `package shared` to match
the module name and directory.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

db.go

@@ -1,4 +1,4 @@
-package shared
+package commons
 
 import (
 	"context"

handle.go

@@ -1,4 +1,4 @@
-package shared
+package commons
 
 import (
 	"net/url"

models.go

@@ -1,4 +1,4 @@
-package shared
+package commons
 
 import (
 	"time"

util.go

@@ -1,4 +1,4 @@
-package shared
+package commons
 
 import (
 	"net/url"