#20445: fix(tools): restore Firecrawl config schema and add FIRECRAWL_BASE_URL env fallback

## Summary `tools.web.fetch.firecrawl` is documented and actively used by `web_fetch`, but the runtime config schema no longer accepts it. That creates a bad user experience: valid Firecrawl config gets rejected up front, and users cannot configure self-hosted Firecrawl endpoints through normal config and env patterns. This PR restores that path and closes a gap in fallback behavior for Firecrawl base URLs. ## What Changed ### Firecrawl config schema and base URL fallback - `src/config/zod-schema.agent-runtime.ts`: Restored `tools.web.fetch.firecrawl` in the runtime schema with expected fields (`enabled`, `apiKey`, `baseUrl`, `onlyMainContent`, `maxAgeMs`, `timeoutSeconds`). - `src/config/config.schema-regressions.test.ts`: Added a schema regression test to lock this shape in place. - `src/agents/tools/web-fetch.ts`: Updated `resolveFirecrawlBaseUrl` to use explicit fallback precedence: `tools.web.fetch.firecrawl.baseUrl` (config), then `FIRECRAWL_BASE_URL` (env), then `DEFAULT_FIRECRAWL_BASE_URL`. - `src/agents/tools/web-fetch.base-url.test.ts`: Added dedicated unit coverage for base URL fallback behavior. - `src/agents/tools/web-tools.fetch.e2e.test.ts`: Added integrated assertions for fallback behavior through the tool execution path. ## Design Notes - The fallback order preserves explicit config as highest priority while still supporting deployment-time env configuration. - The schema update is strict and scoped to known Firecrawl fields, which avoids broadening accepted config unexpectedly. - Coverage is split intentionally between deterministic unit validation and end-to-end execution checks. ## Testing - `pnpm test -- src/agents/tools/web-fetch.base-url.test.ts src/config/config.schema-regressions.test.ts` (Passed: `2` files, `9` tests) - `pnpm exec vitest run --config vitest.e2e.config.ts src/agents/tools/web-tools.fetch.e2e.test.ts -t "(uses FIRECRAWL_BASE_URL env var when firecrawl.baseUrl is unset|falls back to DEFAULT_FIRECRAWL_BASE_URL when config and env are unset)"` (Passed: `2` targeted tests) ## AI Disclosure - [x] AI-assisted - [x] Fully tested ## Related Issues - #2527 - #13146 - #3817 --- Closes #20442 Closes #22256