feat(connect): list server filesystem roots/drives in directory browser (closes #57) (#100)

The directory browser could only descend from a manually-typed path
since the SDK had no way to enumerate the server's filesystem roots
(multiple drives on Windows, mount points, home dir). Add
file.roots() to sdk.ts (GET /file/roots, added server-side in
dzianisv/opencode#238) and show the results as pinned top-level chips
in DirectoryBrowserSheet that jump straight into that root.

Degrades gracefully: older servers 404 on the new endpoint, which the
SDK turns into null, normalizeRoots() turns into an empty list, and
the browser just shows no chips — manual "Jump to path" entry keeps
working exactly as before.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/lib/file-roots.ts

@@ -0,0 +1,40 @@
+// Pure helpers for normalizing GET /file/roots responses from opencode
+// servers. No React Native imports — unit-testable with node --test.
+//
+// Older servers don't expose the endpoint (404), which the SDK client turns
+// into `null`; newer servers may still send malformed, empty-path, or
+// duplicate entries, so this module defends against all of that before the
+// directory browser renders anything.
+
+export interface FileRoot {
+  path: string
+  label: string
+}
+
+function isPlausibleRoot(value: unknown): value is { path: string; label: unknown } {
+  if (typeof value !== "object" || value === null) return false
+  const candidate = value as Record<string, unknown>
+  return typeof candidate.path === "string" && candidate.path.length > 0
+}
+
+/**
+ * Validate and dedupe a raw /file/roots response into pinned entries for
+ * the directory browser. Drops entries missing a non-empty `path`, falls
+ * back to the path itself when `label` is missing/blank, and drops later
+ * duplicates by path (keeping first-seen order). Non-array input (including
+ * `null`, which the SDK returns for servers that don't support the
+ * endpoint) normalizes to an empty list rather than throwing.
+ */
+export function normalizeRoots(raw: unknown): FileRoot[] {
+  if (!Array.isArray(raw)) return []
+  const seen = new Set<string>()
+  const roots: FileRoot[] = []
+  for (const item of raw) {
+    if (!isPlausibleRoot(item)) continue
+    if (seen.has(item.path)) continue
+    seen.add(item.path)
+    const label = typeof item.label === "string" && item.label.trim() ? item.label : item.path
+    roots.push({ path: item.path, label })
+  }
+  return roots
+}