Add KDoc to the services/toolbox API interfaces

Add the interface level docs that StringProvider, SystemClock and
BuildVersionSdkIntProvider were missing, document ExternalIntentLauncher.launch,
and add the remaining @param entries.

Each doc says why the abstraction exists rather than restating the signature:
these wrap Context, Build.VERSION and the clock so that presenters can be tested
without them.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

services/toolbox/api/src/main/kotlin/io/element/android/services/toolbox/api/intent/ExternalIntentLauncher.kt

@@ -14,5 +14,10 @@ import android.content.Intent
  * Used to launch external intents from anywhere in the app.
  */
 interface ExternalIntentLauncher {
+    /**
+     * Starts the given intent, doing nothing when no installed app can handle it.
+     *
+     * @param intent the intent to hand over to the system.
+     */
     fun launch(intent: Intent)
 }

services/toolbox/api/src/main/kotlin/io/element/android/services/toolbox/api/sdk/BuildVersionSdkIntProvider.kt

@@ -10,6 +10,9 @@ package io.element.android.services.toolbox.api.sdk
 
 import androidx.annotation.ChecksSdkIntAtLeast
 
+/**
+ * Exposes the running Android API level, injected rather than read from `Build.VERSION` so tests can pretend to be on any version.
+ */
 interface BuildVersionSdkIntProvider {
     /**
      * Return the current version of the Android SDK.
@@ -18,6 +21,9 @@ interface BuildVersionSdkIntProvider {
 
     /**
      * Checks the if the current OS version is equal or greater than [version].
+     *
+     * @param version the minimum API level required.
+     * @param result computed and returned only when the requirement is met.
      * @return A `non-null` result if true, `null` otherwise.
      */
     @ChecksSdkIntAtLeast(parameter = 0, lambda = 1)
@@ -29,6 +35,11 @@ interface BuildVersionSdkIntProvider {
         }
     }
 
+    /**
+     * Whether the current OS version is equal or greater than [version].
+     *
+     * @param version the minimum API level to test against.
+     */
     @ChecksSdkIntAtLeast(parameter = 0)
     fun isAtLeast(version: Int) = get() >= version
 }

services/toolbox/api/src/main/kotlin/io/element/android/services/toolbox/api/strings/StringProvider.kt

@@ -11,6 +11,9 @@ package io.element.android.services.toolbox.api.strings
 import androidx.annotation.PluralsRes
 import androidx.annotation.StringRes
 
+/**
+ * Resolves Android string resources outside of Composable and Context-aware code, so presenters stay testable.
+ */
 interface StringProvider {
     /**
      * Returns a localized string from the application's package's
@@ -39,6 +42,10 @@ interface StringProvider {
      * Returns a localized formatted string from the application's package's
      * default string table, substituting the format arguments as defined in
      * [java.util.Formatter] and [java.lang.String.format], based on the given quantity.
+     *
+     * @param resId Resource id for the plurals.
+     * @param quantity The quantity used to select the plural form.
+     * @param formatArgs The format arguments that will be used for substitution.
      */
     fun getQuantityString(@PluralsRes resId: Int, quantity: Int, vararg formatArgs: Any?): String
 

services/toolbox/api/src/main/kotlin/io/element/android/services/toolbox/api/systemclock/SystemClock.kt

@@ -8,6 +8,10 @@
 
 package io.element.android.services.toolbox.api.systemclock
 
+/**
+ * Reads the current time, injected rather than called statically so that tests can control it.
+ */
 fun interface SystemClock {
+    /** The current wall-clock time in milliseconds since the epoch. */
     fun epochMillis(): Long
 }