Add cycle support (issues --cycle current, cycles) #21

Scope

• linear-axi issues --cycle current (optionally --cycle <number>) filtered to the active cycle; verify the IssueFilter cycle comparator shape against the live schema (e.g. cycle: { isActive: { eq: true } }).
• linear-axi cycles [--team KEY]: list recent cycles (number, date range, progress) via the team { cycles } connection.

Acceptance

• issues --cycle current --team LIN shows the active cycle's issues; cycles shows past/current/upcoming cycles.