feat(website): add adopters section to highlight notable projects

Introduces a new /adopters page listing notable OSS projects using Task,
along with an infinite-scroll carousel on the homepage linking to it.
The adopter list lives in .vitepress/adopters.ts for easy PR-based
submissions; contributing docs explain the process.

website/src/adopters.md

@@ -0,0 +1,8 @@
+---
+title: Adopters
+description:
+  Open source projects that use Task for their build and release workflows.
+layout: page
+---
+
+<Adopters />

website/src/docs/contributing.md

@@ -125,6 +125,20 @@ Reference][cli-reference]. New fields also need to be added to the [Schema
 Reference][schema-reference] and [JSON Schema][json-schema]. The descriptions
 for fields in the docs and the schema should match.
 
+### Adding your project to the Adopters list
+
+If your open source project uses Task as its task runner, feel free to add it to
+the [Adopters page](/adopters). Open a pull request updating
+`website/.vitepress/adopters.ts` with a new entry following the existing format
+(`name`, `url`, `img`). GitHub organization avatars
+(`https://github.com/<org>.png`) work well as logos. For better control, you can
+also drop an SVG in `website/src/public/img/adopters/` and reference it via
+`/img/adopters/<file>.svg`.
+
+Inclusion criteria: the project must be a public open source repository where
+Task is used as the task runner (presence of a `Taskfile.yml` at the root, or
+clearly documented usage).
+
 ### Writing tests
 
 A lot of Task's tests are held in the `task_test.go` file in the project root