Add sort and filter to agent list view

[scion-gteam]

Summary

• CLI: Added --phase, --activity, --template filter flags and --sort, --reverse sort flags to scion list. Validates flag values against known phases/activities. Passes phase filter server-side in hub mode for efficiency.
• Web UI: Added phase filter chips (All/Running/Stopped/Suspended/Error), sortable table headers (Name, Status, Updated), and a sort dropdown for grid view. Filter and sort state persists to localStorage.
• Tests: Added 9 new test functions covering phase/activity/template filtering, name/created sorting, reverse sort, combined filters, empty results, and flag validation.

Closes #71

Test plan

• go test ./cmd/ -run "TestFilter|TestSort|TestValidate" — all 9 new tests pass
• go test ./cmd/ -run "TestDisplayAgents" — all existing tests still pass
• npx tsc --noEmit — TypeScript type checking passes
• Manual: scion list --phase running shows only running agents
• Manual: scion list --sort name sorts alphabetically
• Manual: scion list --sort created --reverse sorts oldest first
• Manual: scion list with no new flags behaves identically to before
• Manual: Web UI phase filter chips show/hide agents correctly
• Manual: Web UI table headers sort on click