feat(FN-3901): add builtin research web-search provider as default

The merge adds a builtin web-search research provider as the default, replacing the need for external research provider configuration and removing the setup gate for builtin defaults. Dashboard settings UX for research defaults was aligned (ResearchView, SettingsModal), CLI research commands were up

Fusion-Task-Id: FN-3901

docs/agents.md

@@ -307,11 +307,11 @@ Expected behavior and boundaries:
 - Agents should use research only when repository/local context is insufficient
 - Queries should stay narrow and task-scoped; avoid open-ended exploration
 - When `experimentalFeatures.researchView` is disabled, sessions do not register `fn_research_*` tools and prompts do not advertise research capabilities
-- If the research surface is enabled but provider setup is incomplete, tools return actionable `setup` responses instead of crashing
+- If the research surface is enabled but an explicitly selected external provider is misconfigured (or web search is explicitly disabled), tools return actionable `setup` responses instead of crashing
 - Durable conclusions should be persisted with `fn_task_document_write` (for example, `key="research"`)
 - Research runs require the project engine to be running for processing; `fn_research_run` creates the run but does not block for completion unless `wait_for_completion` is set
 
-For the full research workflow, provider setup, CLI commands, and API reference, see the [Research guide](./research.md).
+For the full research workflow, builtin-default behavior, optional external provider setup, CLI commands, and API reference, see the [Research guide](./research.md).
 
 ## Built-In Agent Prompt Templates