fix(build): postinstall script patches flowbite-svelte TypeScript optional params

flowbite-svelte ships TypeScript optional-param syntax (x?: string, event?: MouseEvent,
date?: Date) in its dist .svelte files. Vite's esbuild dep pre-bundler processes these
files (via dist/*/index.js re-exports) and fails with "Unexpected '?'" parse errors
whenever the lockfile changes and the dep cache is rebuilt.

- Add scripts/postinstall.mjs: patches 4 specific TypeScript signatures in
  CommandPalette.svelte, ScrollSpy.svelte, and Datepicker.svelte after every npm install.
  Patches are idempotent and targeted — only the ?-in-param-position syntax is removed;
  optional-chaining (?.) in function bodies is untouched.
- Add "postinstall" script to package.json to run it automatically.
- Upgrade flowbite-svelte 1.31.0 → 1.33.1 (both have the same issue; 1.33.1 is current).
- npm update now works without breaking the dev server.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/postinstall.mjs

@@ -0,0 +1,72 @@
+#!/usr/bin/env node
+/**
+ * Postinstall: strip TypeScript optional-param syntax from flowbite-svelte dist files.
+ *
+ * flowbite-svelte ships raw .svelte files with `<script lang="ts">` in its dist.
+ * esbuild (used by Vite's dep pre-bundler) cannot parse TypeScript optional params
+ * like `(x?: string)` or `event?` in function signatures — it fails with
+ * "Unexpected '?'" or "Expected ')' but found '?'" errors.
+ *
+ * The patches below remove only the TypeScript syntax that causes esbuild to fail.
+ * The `?.` optional-chaining calls in function bodies are left untouched (those are
+ * valid JavaScript and handle undefined correctly at runtime).
+ *
+ * This runs automatically via `"postinstall": "node scripts/postinstall.mjs"` and
+ * is safe to re-run — the replacements are idempotent.
+ */
+
+import { readFileSync, writeFileSync, existsSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { resolve } from 'node:path';
+
+const root = fileURLToPath(new URL('..', import.meta.url));
+const dist = resolve(root, 'node_modules/flowbite-svelte/dist');
+
+if (!existsSync(dist)) {
+    console.log('postinstall: flowbite-svelte dist not found, skipping.');
+    process.exit(0);
+}
+
+let patched = 0;
+
+function patch(relPath, from, to) {
+    const file = resolve(dist, relPath);
+    if (!existsSync(file)) return;
+    const original = readFileSync(file, 'utf8');
+    const updated = original.replace(from, to);
+    if (updated !== original) {
+        writeFileSync(file, updated, 'utf8');
+        console.log(`  patched: ${relPath}`);
+        patched++;
+    }
+}
+
+// CommandPalette.svelte: (x?: string) => x?.toLowerCase()...
+// Remove optional type annotation from the `check` helper param.
+patch(
+    'command-palette/CommandPalette.svelte',
+    /\(x\?:\s*string\)/g,
+    '(x)'
+);
+
+// ScrollSpy.svelte: function scrollToSection(itemId: string, event?: MouseEvent)
+// Remove type annotations from both params.
+patch(
+    'scroll-spy/ScrollSpy.svelte',
+    /scrollToSection\(itemId:\s*string,\s*event\?:\s*MouseEvent\)/g,
+    'scrollToSection(itemId, event)'
+);
+
+// Datepicker.svelte: two functions with optional typed params + return-type annotations.
+patch(
+    'datepicker/Datepicker.svelte',
+    /\(date\?:\s*Date\):\s*string/g,
+    '(date)'
+);
+patch(
+    'datepicker/Datepicker.svelte',
+    /\(date1\?:\s*Date,\s*date2\?:\s*Date\):\s*boolean/g,
+    '(date1, date2)'
+);
+
+console.log(`postinstall: flowbite-svelte — ${patched} file(s) patched.`);