feat: add agent middleware hooks for LLM, tools, retriever, and memory with runtime wiring, tests, and examples

[vinodvx]

Description

Adds agent middleware hooks across the execution lifecycle so applications can intercept and modify LLM calls, tool execution, retrieval, and memory operations via WithHooks.

• Hook points: BeforeLLM / AfterLLM, BeforeTool / AfterTool, BeforeRetrieve / AfterRetrieve, BeforeMemoryLoad / AfterMemoryLoad, BeforeMemoryStore / AfterMemoryStore
• Runtime: wired in internal/runtime/base for local and Temporal paths; hook groups fingerprinted for config drift detection
• API: types in internal/hooks, re-exported from pkg/agent; WithHooks(name, AgentHooks) registers named groups
• Example: examples/agent_with_hooks demonstrates PII scrubbing, retrieval filtering, and memory tenant checks
• Docs: Hooks section in README + examples overview

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactor / chore

Related issues

Closes #18

Checklist

• I have run make check
• I have run task examples:all
• I have run make tidy if I added or removed dependencies
• Commit messages follow conventional commits (e.g. feat:, fix:, docs:)
• I have added/updated tests for my changes
• Documentation is updated if needed

[codecov]

Codecov Report

❌ Patch coverage is 77.76141% with 151 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/runtime/base/runtime.go	76.21%	26 Missing and 13 partials ⚠️
internal/hooks/tools.go	34.04%	27 Missing and 4 partials ⚠️
internal/hooks/memory.go	78.40%	11 Missing and 8 partials ⚠️
internal/runtime/temporal/agent_workflow.go	68.00%	16 Missing ⚠️
internal/runtime/base/memory.go	79.62%	8 Missing and 3 partials ⚠️
internal/hooks/llm.go	66.66%	5 Missing and 5 partials ⚠️
internal/hooks/retriever.go	78.72%	5 Missing and 5 partials ⚠️
internal/runtime/base/hooks.go	88.05%	4 Missing and 4 partials ⚠️
internal/runtime/local/agent_loop.go	94.73%	1 Missing and 1 partial ⚠️
internal/runtime/temporal/options.go	0.00%	2 Missing ⚠️
... and 2 more

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