Add --state filter to issue list #15

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.