Fix TaskWing task system bugs and inconsistencies

[josephgoksu]

Summary

• ID Prefix Resolution: tw task show now accepts unique ID prefixes (e.g., task-abc instead of full ID)
• Archived Plan Filtering: tw task list excludes archived plans by default with --include-archived flag
• Silent Error Fix: Task list now properly propagates errors instead of silently returning empty results
• Storage Layer Hardening: Added rows.Err() checks to database query functions
• MCP Schema Standardization: PlanID uses plan_id (snake_case) with planId accepted as deprecated alias
• TaskStatus Formatter: Complete coverage for all 8 status values with graceful fallback

Test plan

• go test ./cmd -run "TestTaskList*|TestTaskShow*" -v - CLI integration tests
• go test ./internal/util -v - ID utility tests
• go test ./internal/memory -run "TestRows|TestPrefix" -v - Storage layer tests
• make test-quick - Full test suite passes
• Manual validation: tw task show task-fa5a resolves correctly, ambiguous prefixes show candidates