feat: --clear-data flag + typed attribute selectors (#48)

* feat(test): add --clear-data flag to clear app data on launch

* test+docs: cover --clear-data flag in CLI parser test and reference

* feat(spec): type AttrSelector with known attribute names

Replace AttrSelector = Record<string, string> with KnownAttrSelectors
plus a string|boolean index signature, so authors get autocomplete and
type-checking on testTag / focused / clickable / etc. while raw driver
attributes still type-check via the fallback. Boolean state attributes
accept native booleans; goja stringifies them at the marshal boundary.

AccessibilityElement.attrs becomes RawAttrs (typed string-valued shape
of the same canonical names) so element.attrs.testTag autocompletes.

* test(verifier): native boolean selector value matches focused=true

* docs+folio: use native boolean for focused selector and document typed attrs

examples/folio/sanderling/spec.ts

@@ -58,7 +58,7 @@ const ledgerRows = extract<LedgerRow[]>(s =>
 const ledgerBalance = extract(s =>
   parseDollarCents(s.ax.find({ testTag: "LedgerBalance" })?.text));
 
-const focusedFieldTag = extract(s => s.ax.find({ focused: "true" })?.id ?? null);
+const focusedFieldTag = extract(s => s.ax.find({ focused: true })?.id ?? null);
 
 const loginEmailField = extract(s =>
   s.ax.find([{ testTag: "LoginScreen" }, { testTag: "LoginEmail" }]));