feat(keys): one-paste harness setup — Claude Code, Codex, OpenCode, Continue, Cline

The "connect your app" card in the API-keys view now leads with auto-setup
scripts for popular coding harnesses, each pre-filled with this gateway's URL
and the freshly created key:

  Claude Code — env exports (the gateway speaks Anthropic /v1/messages
      natively; the protocol is now ON by default, and when a config has it
      off the tab shows a warning with a one-click Enable button)
  Codex — appends a [model_providers.cortiq] block to ~/.codex/config.toml
  OpenCode — writes the provider into opencode.json
  Continue — appends the model to ~/.continue/config.yaml
  Cline — the exact values to paste into the extension settings

The gateway also detects which harnesses are already present on its machine
(binaries across PATH + common install dirs, config files under home) via
GET /admin/api/harnesses: installed tabs get a ✓, and the status line under
the snippet says "installed" or "already configured for this gateway" when
the harness config mentions cortiq. Works on Linux/macOS/Windows.

curl / python / javascript SDK snippets stay as before. 16 new strings in
all 7 languages.

src/config.rs

@@ -757,7 +757,9 @@ impl Default for Config {
                 openai_completions: true,
                 openai_embeddings: true,
                 openai_models: true,
-                anthropic_messages: false,
+                // on by default: the API-keys view ships a Claude Code
+                // auto-setup snippet that targets /v1/messages
+                anthropic_messages: true,
                 mcp: false,
                 native_passthrough: true,
             },