feat: Replace per-run conversationID string with a single options struct on Run, RunAsync, and Stream

[vinodvx]

Description

Replace the per-run conversationID string on Run, RunAsync, and Stream with a single optional options object so future per-call settings can be added without new parameters.

Target release: 0.2.x (breaking change)

Breaking change

API	Before	After
Run	(ctx, input, conversationID string)	(ctx, input, opts *AgentRunOptions)
RunAsync	(ctx, input, conversationID string)	(ctx, input, opts *AgentRunOptions)
Stream	(ctx, input, conversationID string)	(ctx, input, opts *AgentRunOptions)

Before

result, err := a.Run(ctx, prompt, "")
eventCh, err := a.Stream(ctx, prompt, "session-1")
resultCh, approvalCh, err := a.RunAsync(ctx, prompt, "session-1")

## Type of change

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

## Related issues

Closes #24 

## Checklist

- [x] I have run `make lint` and `make test` locally
- [x] I have run `make tidy` if I added or removed dependencies
- [x] Commit messages follow [conventional commits](https://www.conventionalcommits.org) (e.g. `feat:`, `fix:`, `docs:`)
- [x] I have added/updated tests for my changes
- [x] Documentation is updated if needed

[codecov]

Codecov Report

❌ Patch coverage is 97.05882% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
benchmarks/runner.go	0.00%	1 Missing ⚠️

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