Add OpenCode AI client connect support and fix missing favicon

[JasonLandbridge]

Description
This PR adds OpenCode as a first-class connect/disconnect client across backend, CLI, and web UI, and tightens related client UX.

What changed

Backend

• Added opencode to the connect client registry
• Mapped OpenCode config to:
  • config path: ~/.config/opencode/opencode.json on macOS/Linux
  • config section: mcp
• Enforced existing-file policy for OpenCode config
• Restricted OpenCode edits to the mcp subtree only
• Added endpoint-equivalent adoption logic for OpenCode entries
• Added alias-aware disconnect support via server_name
• Added lenient parsing for OpenCode-style trailing-comma JSON configs

API

• Added/covered connect handler behavior for:
  • adopted OpenCode entries returning idempotent success
  • missing OpenCode config returning 400
  • true conflicts still returning 409

CLI

• Included OpenCode in connect command help/registry coverage
• Added CLI test coverage for registry inclusion

Frontend

• Added server_name?: string to connect status typing
• Updated disconnect API calls to send optional alias server_name
• Updated Connect modal to:
  • support alias-aware disconnect
  • refresh status after connect/disconnect
  • render OpenCode with a lightning icon
• Added unit coverage for:
  • OpenCode row rendering
  • icon rendering
  • alias-aware disconnect

Favicon / browser tab icon

• Replaced default Vite favicon usage with project favicon setup
• Added frontend/public/favicon.svg based on assets/logo.svg
• Updated frontend/index.html to use the normal Vite public-asset favicon path

Docs

• Added OpenCode setup/connect documentation

---

Verification

Ran and tested locally

[Dumbris]

Thanks for this — really clean PR. The test coverage is the most thorough we've seen for a Connect client (HTTP handler + service + CLI + frontend), and the round-trip preservation logic in PreservesNonMCPRootKeys is exactly right.

Reviewed against four maintainer concerns and all four pass:

• Backup before modify — every write path (connect.go:202, 285, 354, 438) routes through the existing backupFile() + atomicWriteFile() primitives. No new bypass.
• Popularity ordering — sensible; tier-1 stays at top, OpenCode appended at the end of allClients reads naturally.
• Per-client tests — service-level + HTTP handler + CLI registry + frontend unit. Most-tested client in the repo.
• Scroll — at 8 clients the modal still fits; we'll add max-h-[60vh] overflow-y-auto on ConnectModal.vue:23 separately as we grow the catalog. Not a blocker for this PR.

Blocker — Windows CI: TestConnect_OpenCode_RequiresExistingConfigFile and TestHandleConnectClient_OpenCodeMissingConfigReturns400 fail on windows-amd64 (and the macOS jobs cancel from the same matrix). Root cause: ConfigPath("opencode", homeDir) reads %LOCALAPPDATA% from the real environment on Windows, ignoring the t.TempDir() injection.

Quickest fix is two t.Setenv calls — happy to push a fixup commit on top of your branch if that's easier:

 func TestConnect_OpenCode_RequiresExistingConfigFile(t *testing.T) {
-    svc, _ := testService(t)
+    svc, home := testService(t)
+    t.Setenv("LOCALAPPDATA", filepath.Join(home, "AppData", "Local"))
     _, err := svc.Connect("opencode", "", false)

Same t.Setenv("LOCALAPPDATA", filepath.Join(home, "AppData", "Local")) in internal/httpapi/connect_test.go:64 and TestConnect_OpenCode_PreservesNonMCPRootKeys. Two-test fix, no production code change.

Once Windows is green this is merge-ready — would like to land it ahead of our spec-046 stack (#433, #434) since it's a clean adapter addition. Let me know if you'd prefer to push the fix yourself or want me to do it.

[Dumbris]

Merged — thanks again Jason. Squash-merged into main; landed ahead of the spec-046 stack as planned.

[JasonLandbridge]

@Dumbris Awesome, and thank you for the compliments, the fix and the awesome app!

I had some more ideas of things that might be cool to add, but I will make some issues out of them first to check with you

[Dumbris]

I had some more ideas of things that might be cool to add, but I will make some issues out of them first to check with you
@JasonLandbridge sounds great! I have send a request to you on LinkedIn. My profile https://www.linkedin.com/in/algis-dumbris/
Let me know if you'd like to have a call sometime.