refactor(sdk-android): publish under io.github.priyanshujain.sanderling + ci docs fix (#27)

* refactor(sdk-android): publish under io.github.priyanshujain.sanderling

Move the published Maven coordinates to a sanderling sub-namespace so the
brand is visible in the dependency line (was io.github.priyanshujain:sdk-android).
Sub-namespace is auto-allowed by Sonatype under the verified parent groupId.

* chore: update sdk-android coordinates in folio + docs

Follow the groupId change to io.github.priyanshujain.sanderling:sdk-android.

* ci(docs): use --version flag for d2 install script

The d2 installer accepts --version vX.Y.Z, not --tag. The --tag form
was rejected as "unrecognized flag" on the docs workflow run after
PR #26 merged.

sdk/android/build.gradle.kts

@@ -11,7 +11,7 @@ plugins {
 }
 
 version = findProperty("sanderling.version") as String? ?: "0.0.0-dev"
-group = "io.github.priyanshujain"
+group = "io.github.priyanshujain.sanderling"
 
 android {
     namespace = "dev.sanderling.sdk"
@@ -55,7 +55,7 @@ mavenPublishing {
     )
 
     coordinates(
-        groupId = "io.github.priyanshujain",
+        groupId = "io.github.priyanshujain.sanderling",
         artifactId = "sdk-android",
         version = version.toString(),
     )