Add --state filter to issue list

Context

tangled issue list currently returns all issues regardless of state. As the issue count grows, it becomes useful to filter by state — for example, to see only open issues when triaging, or only closed issues when reviewing completed work.

The gh CLI uses gh issue list --state open|closed|all for this, which is an intuitive and familiar pattern.

Tasks

• Add --state <open|closed|all> option to tangled issue list (default: open to match gh CLI behaviour).
• Pass the state filter through to the API query so only matching issues are fetched, rather than filtering client-side.
• Update --json output to include the state field so callers can distinguish open/closed records.
• Add or update tests to cover each state filter value.

Notes

Defaulting to open (rather than all) matches gh CLI conventions and keeps the default output focused. Users who want to see everything can pass --state all.