Update Copilot effort choices in parameter comparison documentation

[ScottSDWorx]

Problem

docs/development/agent_parameter_comparison.md documents Copilot effort as only
low|medium|high. Current Copilot CLI help advertises:

none, minimal, low, medium, high, xhigh, max.

The stale comparison contributed to callers using an unsupported representation.

Required change

Update the Copilot effort documentation to match the current CLI and the adapter's normalization
behaviour.

Acceptance criteria

• The comparison lists all current Copilot effort choices.
• It explains that AgentShell accepts case-insensitive input and passes lowercase to Copilot.
• Nearby Copilot parameter documentation remains accurate against current copilot --help.