fix: return empty list when template list offset exceeds count

[pranavgundu]

Summary

• template list returned the full unsliced result when --offset was greater than or equal to the number of templates after filtering. Pagination check used opts.Offset < len(allTemplates), so out of range offsets fell through and re-returned everything.
• Fix returns []Template{} immediately when Offset >= len(allTemplates).

Before fix

• runpodctl template list --type official → 13 templates
• runpodctl template list --type official --offset 13 → returned all 13 again (expected [])
• runpodctl template list --type official --offset 99999 → returned all 13 (expected [])

After fix

• --offset 13 → []
• --offset 99999 → []
• --offset 5 → 8 results (in-range still correct)

Test plan

• go test ./...
• go vet ./...
• live e2e against api.runpod.io for offset edge cases above
• go test -tags e2e ./e2e