fix(android): make wheels find-links URL work on Linux CI

Chaquopy's pip --find-links argument was built with a hard-coded
"file:///" prefix plus rootDir.absolutePath. That works on Windows
(paths start with "C:/...", so prefix + path produces three slashes
after "file:") but breaks on Linux (paths start with "/workspace/...",
so prefix + path produces four slashes — pip then parses "workspace"
as the URL's hostname and aborts with
  "ValueError: non-local file URIs are not supported on this platform".

Pick the prefix based on whether the absolute path already starts with
"/", so we always end up with exactly three slashes between "file:" and
the drive letter or root.

android/app/build.gradle.kts

@@ -119,9 +119,17 @@ chaquopy {
         version = "3.11"
 
         pip {
-            // Pre-built wheels directory (for pydantic-core etc.)
-            // Must use absolute file:// URI with forward slashes
-            options("--find-links", "file:///${rootDir.absolutePath.replace("\\", "/")}/wheels/")
+            // Pre-built wheels directory (for pydantic-core etc.) as an
+            // absolute file:// URI with forward slashes. Pip requires
+            // exactly three slashes after `file:` for an empty-host local
+            // path; the path-normalization differs by platform:
+            //   Windows: absolute path is "C:/..."  → prefix "file:///"
+            //   Linux:   absolute path is "/..."    → prefix "file://"
+            // Using a fixed "file:///" prefix on both made CI produce
+            // "file:////workspace/…", which pip rejects as non-local.
+            val wheelsPath = rootDir.absolutePath.replace("\\", "/")
+            val wheelsUrlPrefix = if (wheelsPath.startsWith("/")) "file://" else "file:///"
+            options("--find-links", "$wheelsUrlPrefix$wheelsPath/wheels/")
 
             // ── Android-compatible dependencies ─────────────────
             // Listed explicitly because pyproject.toml includes