docs(readme): refine benchmark and architecture visuals

[Yofuria]

Summary

• replace Efficient Context with Less Tokens in the benchmark headline
• replace the Architecture diagram with the refined compact version
• fix label overlap and text overflow in the updated Architecture SVG

Validation

• ruff check .
• ruff format --check .
• Architecture and benchmark SVG files parsed successfully
• git diff --check origin/main...HEAD

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Route the context manager only to the HTTP service

In the README architecture diagram, this new branch runs from the BCG Context Manager directly into the Python SDK, even though the manager always constructs BcgClient and sends evicted turns to the HTTP /turns endpoint (agent-cli/src/core/context/bcg-context.ts:588, agent-cli/src/core/context/bcg-client.ts:39-49). The SDK is a separate direct-backend integration, as the SVG description itself states, so readers following this diagram may incorrectly expect the bundled Agent context manager to support an SDK/in-process path; remove this branch or originate it from a separate SDK consumer.

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