Add the Godot plugin, with a README spotlight - #288

Adds the Godot editor plugin to the catalog and spotlights it in the README. This is the catalog side of #284; the listing itself is still pending, so #284 stays open.

The plugin: https://github.com/TMHSDigital/free-game-dev-assets-godot, released as v0.1.0.

Changes

• New entry catalog/tools/free-game-dev-assets-godot.md: MIT, active, licence quoted from LICENSE at the v0.1.0 tag. Its first Notes line says the catalog's maintainers made it, so readers can weigh that.
• README spotlight in the Godot section: a screenshot of the dock (loaded from the plugin repo's tagged image, so no image file is added here) with a short description.
• catalog/tools/README.md: a row in the index and in the Godot 4 add-ons maintenance table (4.3+, v0.1.0, pre-1.0).
• docs/godot-budget-stack.md: a row in the add-ons table, and a paragraph under Hygiene on tracking credits with it.
• Counts synced with npm run counts: 420 listed entries, 122 tools.

Checks

• npm run check passes locally (lint, tests, validate, check-added, build).

Follow-ups not in this PR

• npm run counts asks for docs/images/readme/og-card.png to be retaken after the next build, because the count on the card changed.
• Godot plugin: release, list in the Godot Asset Library, and link from the README #284 also asks for a mention on the site's Godot pages. The entry shows up on the site through the normal build; anything more prominent there is a separate change.
• Once the Asset Library listing is approved: link it from this entry and the README, close Godot plugin: release, list in the Godot Asset Library, and link from the README #284, then close bigger bet: browse the catalog from inside Godot (then Unity / Unreal) with an editor plugin #116 with Unity and Unreal left as future ideas.

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