fix(setup): treat empty DSH_HOME as unset (#2686)

* fix(setup): treat empty DSH_HOME as unset (#2666)

The released `@deepseek-ai/dsh-home-paths` package explicitly treats an
empty or whitespace-only `DSH_HOME` as unset and selects the default
Harness home patch. `dshHomeDirectory` previously used nullish coalescing
(`env.DSH_HOME ?? join(home, ".dsh")`), so an empty override flowed
straight through `join(..., "cordis.patch.yml")` and produced a
cwd-relative `cordis.patch.yml` outside the client-selected home.

Treat empty and whitespace-only overrides as unset, matching the sibling
OpenCode override resolver and the released DSH resolver. The patch now
lands at `$DSH_HOME/cordis.patch.yml` for explicit overrides, the default
`~/.dsh/cordis.patch.yml` for empty/unset, and trimmed whitespace for
padded overrides.

Adds `src/application/SupportedClients.test.ts` covering the empty,
whitespace-only, unset, padded, and explicit cases via the public
`supportedClients(...)` entrypoint. Fixes #2666.

* test(setup): remove superseded DSH path unit coverage

---------

Co-authored-by: morluto <76467478+morluto@users.noreply.github.com>

src/application/SupportedClients.ts

@@ -539,7 +539,7 @@ export const SUPPORTED_CLIENT_DEFINITIONS = [
     configPath: ({ home, platform, env }: ClientPathContext) =>
       join(devinDirectory({ home, platform, env }), "mcp_config.json"),
     markerPath: devinDirectory,
-    format: "json",
+    format: "devin",
   },
   {
     name: "opencode",