fix(mindspace): lower page access password minimum to 6 characters

Align publication validation, portal gate HTML, H5 publish UI, MCP docs,
and page-data skill guidance so passwords like 888888 are accepted while
3-character values such as 888 remain rejected.

Co-authored-by: Cursor <cursoragent@cursor.com>

mindspace-publications.test.mjs

@@ -110,6 +110,7 @@ test('hashes access passwords with a random salt', () => {
     () => publicationInternals.normalizePassword('short', true),
     (error) => error.code === 'invalid_publish_input',
   );
+  assert.equal(publicationInternals.normalizePassword('888888', true), '888888');
 });
 
 test('requires future expiry timestamps for time-limited pages', () => {