#7252: docs: align config examples and tool docs with current runtime

Fixes documentation drift vs current runtime: - Update legacy config examples from `agent.*` to `agents.defaults.*` - Clarify browser tool actions vs CLI-only profile management - Document process `send-keys` - Clarify exec params and tool availability gating (`cron`/`gateway`/`message` depend on tool profile + allow/deny) Documentation-only; no runtime behavior changes. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates documentation examples and tool reference text to match the current runtime configuration schema and tool policy. Key changes: - Migrates legacy config snippets from `agent.*` to `agents.defaults.*` across concepts, gateway configuration/examples, and getting-started docs. - Updates tools documentation to reflect current tool group membership (`group:runtime` is `exec` + `process`), clarifies browser profile management as CLI-only, and documents additional tool action/availability notes (message/cron/gateway). No runtime behavior is changed; these edits reduce doc drift and align examples with the actual config schema used by the gateway/agent runtime. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge; it’s documentation-only and appears consistent with the current runtime schema/tooling. - Reviewed the diffs for all changed docs and spot-checked against the current codebase: the `agents.defaults` schema matches runtime, `group:runtime` membership matches tool policy (with `bash` as an alias rather than a separate tool), and the browser profile management clarification aligns with CLI behavior. No broken syntax or contradictory guidance was found in the touched sections. - No files require special attention <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} **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 -->