docs(tealtiger): add Haystack 3.0 Agent Hooks support (before_tool governance)

[nagasatish007]

Updates the TealTiger integration page to document Haystack 3.0 Agent Hooks support (v0.2.0 of tealtiger-haystack).

What changed

• Added TealTigerGovernanceHook usage example as the recommended approach for agents (Haystack 3.0+)
• Existing pipeline component examples remain unchanged (backward compatible with 2.x)
• Added new features: secret detection, tool authorization (allowlist/denylist), serialization support
• Updated version field from Haystack 2.0 to Haystack 2.0+

Why

Haystack 3.0 introduced Agent Hooks (before_tool, after_tool) as the native extension point for agent-level middleware. TealTiger's governance is a natural fit for before_tool — enforce PII scanning, tool authorization, and cost budgets before any tool executes.

The existing pipeline component approach still works but is limited to query-level governance. The hooks approach provides tool-call-level governance inside the agent loop.

Package

• PyPI: https://pypi.org/project/tealtiger-haystack (v0.2.0)
• Source: https://github.com/agentguard-ai/tealtiger/tree/main/packages/haystack-tealtiger

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[nagasatish007]

@kacperlukawski Please review . This is an update for previously approved PR.