refactor(code-executor): migrate user scripts to single context argument

- replace (page, context, helpers) signature with async (context) => {}
- add ScriptContext interface exposing page, browser, env, getEnv,
  getCredential, getStepOutput, runSnippet, dumpDom, log/warn/error
- rename getEnvUrl to getEnv throughout service and docs
- fix step ordering: normalizeStepOrder and run step rows are now 1-based
- migrate existing DB rows (scenario_steps, scenario_run_steps) +1
- update all tests and stored snippet/step code in DB to new API

server/src/browser/browser.service.ts

@@ -187,16 +187,15 @@ export class BrowserService {
         this.logger.log(`[${label}] exec: running user code`);
         const scriptLogger: ScriptLogger = (level, msg) =>
           this.logger[level](`[${label}] script: ${msg}`);
-        const result = await this.codeExecutor.execute(
+        const result = await this.codeExecutor.execute({
           page,
-          context,
+          browser: context,
           code,
-          scriptLogger,
-          undefined,
+          log: scriptLogger,
           credentials,
           environment,
           snippets,
-        );
+        });
         this.logger.log(`[${label}] exec: done`);
         return result;
       } catch (err) {
@@ -208,13 +207,17 @@ export class BrowserService {
     const snippetMap = await this.snippetService
       .buildSnippetMap()
       .catch(() => ({}) as Record<string, string>);
+
+    // TODO: instantiate one browser per server instance and reuse contexts for anonymous sessions, 
+    // instead of launching a new browser for each request.
     const browser = await chromium.launch({
       headless: true,
       executablePath: process.env.PLAYWRIGHT_CHROMIUM_EXECUTABLE_PATH,
     });
+
     try {
-      const context = await browser.newContext();
-      const page = await context.newPage();
+      const browserContext = await browser.newContext();
+      const page = await browserContext.newPage();
 
       if (url) {
         this.logger.log(`[${label}] exec: navigating to ${url}`);
@@ -224,16 +227,15 @@ export class BrowserService {
       this.logger.log(`[${label}] exec: running user code`);
       const scriptLogger: ScriptLogger = (level, msg) =>
         this.logger[level](`[${label}] script: ${msg}`);
-      const result = await this.codeExecutor.execute(
+      const result = await this.codeExecutor.execute({
         page,
-        context,
+        browser: browserContext,
         code,
-        scriptLogger,
-        undefined,
+        log: scriptLogger,
         credentials,
         environment,
-        snippetMap,
-      );
+        snippets: snippetMap,
+      });
       this.logger.log(`[${label}] exec: done`);
       return result;
     } catch (err) {

server/src/browser/dto/exec.dto.ts

@@ -31,7 +31,7 @@ export class ExecDto {
 
   @ApiPropertyOptional({
     description:
-      "Key/value map of environment variables available via `helpers.env` and `helpers.getEnvUrl()` in the script.",
+      "Key/value map of environment variables available via `helpers.env` and `helpers.getEnv()` in the script.",
     example: { BASE_URL: "https://example.com" },
   })
   @IsOptional()