Cover both scoring modes, verbose output, limit, empty case, and JSON
output. Update SKILL.md and README.md.

Add next to cli.rs, cmd/next.rs, and cmd/mod.rs. Queries open tasks and
blocker edges from the DB, feeds them to score::rank(), and renders
results using comfy-table with a header row.

Add src/score.rs with the core algorithm for the next command: build the
blocker DAG from open tasks, compute transitive downstream scores, and
rank ready tasks using mode-dependent formulas.

show displays all blocker edges regardless of status, making tasks appear
blocked when their blockers are closed. Split the display into open
blockers (actually blocking) and resolved ones.

list and ready display priority and effort as bare low/medium/high in
adjacent columns with nothing distinguishing them. Add a header row to
each using comfy-table's set_header().

Replace hardcoded format!() spacing with comfy-table across all commands.
Fix missing effort column in list output.

Prevent circular dependencies in the blocker graph by walking the existing
edges from the proposed blocker back toward the task. Reject with a clear
error if a cycle would be created.

jj hard