docs(browser): add multi-turn consult guardrails

[pdurlej]

Summary

• document when agents should choose one-shot browser consults, explicit browser follow-ups, or Deep Research
• add a dry-run note when explicit browser follow-ups are present, clarifying that Oracle sends only caller-provided follow-up prompts
• keep the change guidance-only: no automatic follow-up generation, no browser DOM changes, no model-picker/composer changes, and no Project Sources behavior changes

Tests

• pnpm install --frozen-lockfile
• pnpm vitest run tests/cli/dryRun.test.ts tests/mcp/consult.test.ts tests/browser/index.test.ts tests/browser/sessionRunner.test.ts -> 4 files passed, 47 tests passed
• pnpm run check
• pnpm run build
• pnpm test -> 115 files passed, 18 skipped; 788 tests passed, 41 skipped
• git diff --check

Notes

This intentionally avoids selector/composer/model-selection code so it does not overlap with #176/#177. It also avoids any fixed quality-uplift claim; the docs ask users to compare concrete review differences instead.