#8252: Config: honor legacy memorySearch alias

## Summary - accept top-level `memorySearch` in config schema and merge it into `agents.defaults.memorySearch` when defaults are missing - add unit coverage for legacy alias mapping behavior - note the canonical config location in memory docs ## Testing - `pnpm vitest run --config vitest.unit.config.ts src/config/config.memory-search-legacy-alias.test.ts` <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adds support for a legacy config alias `memorySearch` at the top level of the OpenClaw config. The schema now accepts `memorySearch`, `applyAgentDefaults` merges it into `agents.defaults.memorySearch` only when `agents.defaults.memorySearch` is not already set, and unit tests cover both the merge behavior and the non-overriding case. Documentation is updated to point users at the canonical `agents.defaults.memorySearch` location while noting the legacy alias. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - Changes are narrowly scoped to config schema acceptance and default-merging logic for a legacy alias, with explicit unit tests validating the intended precedence rules. The new top-level schema field is optional and the merge only occurs when canonical defaults are absent. - No files require special attention <!-- greptile_other_comments_section --> _{(5/5) You can turn off certain types of comments like style [here](https://app.greptile.com/review/github)!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment --> ## AI-Assisted Yes — implemented and reviewed with AI assistance. ## Local Validation ```bash pnpm build && pnpm check && pnpm test ``` All tests pass. TypeScript compilation clean. Lint passes.