feat(agentHost): implement custom agent picker and refactor related components (#317719)

* feat(agentHost): implement custom agent picker and refactor related components

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* docs(agentHost): clarify resolveAgentHostAgent JSDoc URI types

Co-authored-by: DonJayamanne <1948812+DonJayamanne@users.noreply.github.com>

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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>