When Japanese translation files don't exist (e.g. versions before v5.9),
fall back to English titles instead of crashing with FileNotFoundError.
Also skip move_manual when source/target doesn't exist.

When a language's md file doesn't exist, skip the entry entirely
rather than falling back to English titles. This avoids generating
sidebar/nav entries for unsupported languages (e.g. ja before v5.9).

Detect supported languages by checking if language directories have
real doc content (not just auto-generated configuration manual).
Versions before v5.9 without ja_JP docs will no longer produce
ja entries in directory.json.

shutil.copyfile fails when the target directory doesn't exist
(e.g. fresh clone without residual files from other branches).

Configuration manual is no longer generated via move_manual.
Remove the function, shutil import, cfg-manual-docgen/ directory,
and clean up typos exclude list.

…ement

…qx/emqx-docs into 260310-config-horizontal-menu