docs: update README and MCP_INTEGRATION for v2.1.0 agent-native tools

[Anandb71]

Add 10-tool inventory, standard envelope description, suggested_next_tool chaining explanation, and get_callers example to MCP_INTEGRATION.md. README What-you-get and MCP section updated to reflect v2.1.0.

Description

Brief description of what this PR does. Link any related issues.

Fixes #(issue number)

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Performance improvement
• Code refactoring

Changes Made

• List the key changes made in this PR
• Be specific about files/modules affected

Testing

Describe how you tested your changes:

• Ran cargo test --all
• Ran cargo clippy --all
• Ran flutter test (if applicable)
• Tested manually with a real codebase

Screenshots (if applicable)

For visualizer changes, include before/after screenshots.

Checklist

• My code follows the project's style guidelines
• I have added tests for my changes
• I have updated the documentation where necessary
• All new and existing tests pass
• I have added appropriate comments where the code isn't self-explanatory

[github-actions]

Arbor Graph Impact Report

Blast Radius: High-centrality nodes affected?

2026-05-05T10:13:41.239384Z INFO Starting index of /home/runner/work/arbor/arbor
2026-05-05T10:13:41.240685Z WARN Failed to parse /home/runner/work/arbor/arbor/arbor-impact.md: file is empty: '/home/runner/work/arbor/arbor/arbor-impact.md'
2026-05-05T10:13:41.413278Z INFO Indexed 104 files, 0 cache hits (1600 nodes) in 173.898621ms
Change Impact Preview

Modified files:
• README.md
• docs/MCP_INTEGRATION.md

Impact:
• 0 direct callers
• 0 indirect callers
• 0 API entrypoints affected
• 0 files likely require updates
• 0 impacted nodes total
• 111 changed symbols resolved

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