feat(chunks): keep chunk code in files, deprecate the database column

[elcreator]

A chunk's code now lives in views/chunks/.html. The file is the chunk if it exists; the site_htmlsnippets column is what a chunk nobody has saved since holds, and the mirror the manager's search still reads. Both readers - the parser on demand and the site cache builder, which short circuits it - go through one rule, so a cached chunk does not render the stale column.

No column, no setting and no migration: a site crosses over one save at a time and one that saves nothing keeps rendering what it always did. Every database path is marked @deprecated since 3.5.8 with @todo [remove@3.7], so artisan deprecated:list collects them.

Under views/, not assets/: the root .htaccess passes ^assets/ straight to the filesystem, and chunks are where older extras keep configuration. Verified against Apache - a file under assets/chunks came back 200 with its contents, the same file under views/ came back 403. The directory ships with deny guards, and the store writes them wherever it is pointed.

Chunk names are prose, so hazardous bytes are percent-encoded rather than the name refused, and decoded back exactly: "nav/main" is nav%2Fmain.html, "CON" is %43ON.html, "Кнопка" stays readable. What encoding cannot fix is refused with a reason - invalid UTF-8, not NFC, too long once escaped, or a name that would share one file with another chunk on a case-insensitive filesystem. The form previews the same encoding the store applies.

Renaming or deleting a chunk takes its files with it; one left behind would be adopted silently by the next chunk named the same.