docs: rebrand Windsurf doc page to Devin Desktop - #28205

## Summary

Cognition rebranded the Windsurf Editor as Devin Desktop on June 2, 2026
(Cognition acquired Windsurf from Codeium in July 2025). This adds a
`devin-desktop` module using the current name, without breaking the
existing `windsurf` module.

## Backward compatibility approach

The Terraform module registry protocol has no rename/alias mechanism
(`registry-server`'s own code comments confirm this: "the registry
server has no alias mechanism for the old path"). Renaming `windsurf`'s
directory/slug would break every template pinned to
`registry.coder.com/coder/windsurf/coder`, so this PR is purely
additive:

- **`windsurf` module: unchanged behavior.** Only its README gets a
`[!IMPORTANT]` notice pointing to `devin-desktop`. It stays published
and fully functional for existing templates.
- **New `devin-desktop` module**, matching the same pattern already used
by every other desktop-IDE module in this registry (`cursor`, `zed`,
`windsurf`, etc.): a thin wrapper around the shared
`vscode-desktop-core` module, so none of the actual
`coder_app`/deep-link logic is duplicated beyond what's already
duplicated across that whole module family today.

I considered having `devin-desktop` delegate directly to the `windsurf`
module (even less duplication), but that requires bumping `windsurf` to
a new tagged version first, module registry composition resolves against
already-published versions, and tags are only cut by a maintainer after
merge (see `MAINTAINER.md`). That would force two sequential PRs with a
manual tagging step in between for no real benefit given how small the
`vscode-desktop-core` wiring is, so I went with the direct wrapper
instead.

## Icon

Added a dedicated `devin.svg` (`.icons/devin.svg`), a monochrome vector
of Cognition's Devin mark, adapted from the MIT-licensed
[`@lobehub/icons-static-svg`](https://www.npmjs.com/package/@lobehub/icons-static-svg)
package (`icons/devin.svg`), recolored to `#fff` to match this
registry's existing monochrome icon convention (e.g. `windsurf.svg`).
Named `devin`, not `devin-desktop`, matching how this registry already
names icons/tags after the umbrella brand rather than the specific
product surface (e.g. `claude-code` module uses `claude.svg`/`claude`
tag). The module id/slug stays `devin-desktop` though, kept specific
because Cognition's Devin family also includes Devin Local/Cloud/Review,
a bare `devin` module name would be ambiguous between the desktop IDE
launcher (this module) and a future CLI-agent-style module.

## ⚠️ Merge sequencing

This module defaults to opening Devin Desktop via a `devin://` deep link
(placeholder, not independently verified against a live install).
Opening `devin://` links requires `"devin:"` to be registered in Coder's
`ALLOWED_EXTERNAL_APP_PROTOCOLS`, see
[coder/coder#28214](coder/coder#28214). **Do not
tag/release this module until #28214 ships in a released Coder
version**, otherwise the module's "Open" button is broken (unsubstituted
session token) on any deployment running an older Coder. The `protocol`
input can be overridden (e.g. back to `"windsurf"`) in the meantime if
needed.

## Known gap (flagging for review)

Devin Desktop is documented by Cognition as backwards-compatible with
Windsurf (same `~/.codeium/windsurf/` config path), but I haven't
verified this hands-on against the actual app.

## Validation

- `terraform init -upgrade` and `terraform validate` pass against the
live registry.
- `bun test registry/coder/modules/devin-desktop/main.test.ts`: 10/10
pass (mirrors `windsurf`'s test coverage, plus cases for overriding
`slug`/`display_name`/`protocol`).
- `terraform fmt -check`, `bun run fmt`: clean for this module
(repo-wide `terraform fmt -recursive` currently panics for unrelated
pre-existing reasons; scoped `terraform fmt -check -diff` on this
module's directory passes).
- `go build ./cmd/readmevalidation && ./readmevalidation`: passes (81
modules including the new one, all relative URLs and icon paths valid).

Related: [coder/coder#28205](coder/coder#28205)
(docs rebrand, now links to this module),
[coder/coder.com#1014](coder/coder.com#1014)
(redirect),
[coder/coder#28206](coder/coder#28206) (Devin
icon), [coder/coder#28214](coder/coder#28214)
(URI scheme allowlist, blocking).

> 🤖 This PR was created with the help of Coder Agents, and needs a human
review. 🧑💻

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Co-authored-by: DevCats <[email protected]>