Add en-tech preset

[misaochan]

Fixes #671 .

Added en-tech preset with 12 Stack Exchange sites and all 231 English Devdocs zims.

I only selected Stack Exchange sites that were relevant and had valid menu defs. Devdocs zims all don't have menu defs, so after install they can be browsed via Kiwix, but they don't get individual home page tiles.

Tested by running an install and confirmed all 243 items were scheduled.

Tested on: Ubuntu 26.04 LTS, Python 3.14.4

[tim-moody]

The standard for a preset is that all content appears on the home menu. If you let the preset install it will generate menu defs, though the titles will default to what Kiwix has and so may not be unique.

I admit a menu with 243 items is rather large, but on a default IIAB all this content will get added to the menu. (I think the preset menu is copied early, so will get modified.)

"autoupdate_menu": true governs this.

Another approach would be to add en-kiwix-devdocs to the home page which just goes to Kiwix home.