RTECO-1074 - Remove redundendent functions in agent namespace(1/2)

[udaykb2]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• All static analysis checks passed.
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Summary

Removes wrapper functions that were duplicating logic between agent/plugins/common and agent/skills/common. Specifically:

• Moved ResolveAgentTargets, CopyExtractedToTargets, and related helpers up to agent/common (the single source of truth)
• Deleted the per-namespace copies in plugins/common and skills/common
• Updated all callers in install.go, update.go, list.go to call agentcommon.* directly
• Moved tests to agent/common