feat(l10n): single-source localization pipeline

Add localization/ — one strings.json is the source of truth for every
user-facing string, and a Bun CLI generates the platform files:

  loc migrate   rebuild strings.json from existing platform files (one-time)
  loc validate  structural checks (plural `other`, arg refs, coverage)
  loc generate  emit .xcstrings (Apple) + per-language strings.xml (KMP)

Canonical `{name}` placeholders are converted to each platform's positional
printf tokens using declared arg types. Plurals use CLDR categories and emit
native forms: xcstrings plural variations and Compose <plurals> blocks.

Migration folds the KMP `transfer_file_count_one`/`_other` pair into a single
plural key, so `transferFileCountResource` now returns the plural resource and
callers resolve it with pluralStringResource.

localization/src/commands/generate.ts

@@ -0,0 +1,97 @@
+/**
+ * Generate platform files from strings.json:
+ *   - Apple: one Localizable.xcstrings (all languages nested).
+ *   - KMP:   one values[-lang]/strings.xml per supported language.
+ */
+import { mkdirSync } from "node:fs";
+import { join } from "node:path";
+import {
+  APPLE_XCSTRINGS,
+  kmpValuesDir,
+  KMP_RESOURCES,
+  STRINGS_JSON,
+} from "../config";
+import { renderAndroid, type ParsedAndroid } from "../lib/android-xml";
+import { fromCanonical, type Flavor } from "../lib/placeholders";
+import { renderXcstrings, type XcCatalog, type XcEntry } from "../lib/xcstrings";
+import { targetsOf, type StringEntry, type StringsFile } from "../types";
+
+function render(entry: StringEntry, text: string, flavor: Flavor): string {
+  return fromCanonical(text, entry.args ?? [], flavor);
+}
+
+// ---- Apple ------------------------------------------------------------------
+
+function buildXcstrings(doc: StringsFile): XcCatalog {
+  const strings: Record<string, XcEntry> = {};
+
+  for (const [key, entry] of Object.entries(doc.strings)) {
+    if (!targetsOf(entry).includes("apple")) continue;
+    const xc: XcEntry = { extractionState: "manual" };
+    if (entry.context) xc.comment = entry.context;
+    const localizations: XcEntry["localizations"] = {};
+
+    for (const lang of doc.supportedLanguages) {
+      const state = lang === doc.sourceLanguage ? "translated" : "needs_review";
+      if (entry.plural) {
+        const forms = entry.plural[lang];
+        if (!forms) continue;
+        const plural: Record<string, { stringUnit: { state: any; value: string } }> = {};
+        for (const [cat, value] of Object.entries(forms)) {
+          plural[cat] = { stringUnit: { state, value: render(entry, value, "apple") } };
+        }
+        localizations[lang] = { variations: { plural } };
+      } else {
+        const value = entry.translations?.[lang];
+        if (value === undefined) continue;
+        localizations[lang] = { stringUnit: { state, value: render(entry, value, "apple") } };
+      }
+    }
+
+    if (Object.keys(localizations).length) xc.localizations = localizations;
+    strings[key] = xc;
+  }
+
+  return { sourceLanguage: doc.sourceLanguage, strings, version: "1.0" };
+}
+
+// ---- KMP --------------------------------------------------------------------
+
+function buildAndroid(doc: StringsFile, lang: string): ParsedAndroid {
+  const out: ParsedAndroid = { strings: [], plurals: [] };
+
+  for (const [key, entry] of Object.entries(doc.strings)) {
+    if (!targetsOf(entry).includes("kmp")) continue;
+    if (entry.plural) {
+      const forms = entry.plural[lang];
+      if (!forms) continue;
+      const items: Record<string, string> = {};
+      for (const [cat, value] of Object.entries(forms)) {
+        items[cat] = render(entry, value, "android");
+      }
+      out.plurals.push({ name: key, items });
+    } else {
+      const value = entry.translations?.[lang];
+      if (value === undefined) continue;
+      out.strings.push({ name: key, value: render(entry, value, "android") });
+    }
+  }
+  return out;
+}
+
+// ---- entry ------------------------------------------------------------------
+
+export async function generate() {
+  const doc = JSON.parse(await Bun.file(STRINGS_JSON).text()) as StringsFile;
+
+  await Bun.write(APPLE_XCSTRINGS, renderXcstrings(buildXcstrings(doc)));
+  console.log(`Wrote ${APPLE_XCSTRINGS}`);
+
+  for (const lang of doc.supportedLanguages) {
+    const dir = join(KMP_RESOURCES, kmpValuesDir(lang, doc.sourceLanguage));
+    mkdirSync(dir, { recursive: true });
+    const file = join(dir, "strings.xml");
+    await Bun.write(file, renderAndroid(buildAndroid(doc, lang)));
+    console.log(`Wrote ${file}`);
+  }
+}