fix: make Codex TOML base_url editing section-aware

Rewrite setCodexBaseUrl/extractCodexBaseUrl to understand TOML section
boundaries, ensuring base_url is written into the correct
[model_providers.<name>] section instead of being appended to file end.

- Add section-aware TOML helpers in providerConfigUtils.ts
- Extract shared update_codex_toml_field/remove_codex_toml_base_url_if
  in codex_config.rs, deduplicate proxy.rs TOML editing logic
- Replace scattered inline base_url regexes with extractCodexBaseUrl()
- Add comprehensive tests for both Rust and TypeScript implementations

src/components/providers/AddProviderDialog.tsx

@@ -17,6 +17,7 @@ import { UniversalProviderPanel } from "@/components/universal";
 import { providerPresets } from "@/config/claudeProviderPresets";
 import { codexProviderPresets } from "@/config/codexProviderPresets";
 import { geminiProviderPresets } from "@/config/geminiProviderPresets";
+import { extractCodexBaseUrl } from "@/utils/providerConfigUtils";
 import type { OpenClawSuggestedDefaults } from "@/config/openclawProviderPresets";
 import type { UniversalProviderPreset } from "@/config/universalProviderPresets";
 
@@ -179,11 +180,9 @@ export function AddProviderDialog({
         } else if (appId === "codex") {
           const config = parsedConfig.config as string | undefined;
           if (config) {
-            const baseUrlMatch = config.match(
-              /base_url\s*=\s*["']([^"']+)["']/,
-            );
-            if (baseUrlMatch?.[1]) {
-              addUrl(baseUrlMatch[1]);
+            const extractedBaseUrl = extractCodexBaseUrl(config);
+            if (extractedBaseUrl) {
+              addUrl(extractedBaseUrl);
             }
           }
         } else if (appId === "gemini") {