feat: replace catwalk with models.dev, auto-route openai-compatible providers, fix all lint issues

Replace catwalk dependency with direct models.dev integration (97 providers,
3039 models vs catwalk's 22/679). Auto-route @ai-sdk/openai-compatible
providers through fantasy's openaicompat using the api URL from models.dev,
eliminating the need for --provider-url. Add --all flag to 'mcphost models'
to show all providers vs just fantasy-compatible ones.

Fix all 74 golangci-lint issues: errcheck (53), staticcheck SA4006 (24),
SA9003 (2), ST1005 (5), ineffassign (3). Restructure styles.go color
handling into a colorScheme struct to eliminate SA4006 false positives
from new(x) syntax.

btca.config.jsonc

@@ -36,8 +36,14 @@
       "name": "catwalk",
       "url": "https://github.com/charmbracelet/catwalk",
       "branch": "main"
+    },
+    {
+      "type": "git",
+      "name": "crush",
+      "url": "https://github.com/charmbracelet/crush",
+      "branch": "main"
     }
   ],
   "model": "claude-haiku-4-5",
   "provider": "opencode"
-}
+}