Add richer filters to `issues list`

[dubscode]

Summary

Please add first-class filtering options to linear issues list so agents and scripts can narrow results without broad workspace scans and ad hoc post-processing.

This is adjacent to #3, which asks specifically for parent/child filtering. This issue is for the broader common Linear filters.

Proposed flags

Useful initial set:

linear issues list --state Backlog --json
linear issues list --assignee me --json
linear issues list --project "Evalite setup" --json
linear issues list --label eng --json
linear issues list --priority 2 --json
linear issues list --query "evalite" --json
linear issues list --updated-after 2026-05-01 --json
linear issues list --created-after -P7D --json
linear issues list --no-parent --json

Why this matters

The CLI already has JSON output and canonical branch-name support, which makes it promising for agent workflows. But without filters, callers have to list recent workspace issues and grep locally, which is brittle across large workspaces and especially confusing when multiple projects share similar issue titles.

Expected behavior

• Filters should compose where Linear supports it.
• Help output should document the flags.
• JSON output should remain stable and paginated via existing --limit / --cursor behavior.
• Identifiers and human names should be accepted where practical, matching the current friendly style of commands like linear issues get <id> and linear issues branch <id-or-identifier>.

[dubscode]

This was generated by AI during triage.

Agent Brief

Category: enhancement
Summary: Finish richer filtering support for linear issues list.

Current behavior:
The CLI already has several global list filters such as project, cycle, state, assignee, label, priority, free-form filter, sorting, all-pages draining, and mine-only filtering. The original issue is therefore partially satisfied, but useful filters remain missing or unclear.

Desired behavior:
linear issues list should support the remaining common filters needed for agent/script workflows, especially text search, created/updated date windows, and top-level-only filtering. Existing filters should remain backward-compatible and documented.

Key interfaces:

• Issue list options should support query, updated-after, created-after, and no-parent semantics.
• Filtering should compose with existing pagination, sorting, and JSON output behavior.
• Date filters should accept clear documented formats, including ISO dates. Relative duration support is nice only if it fits existing conventions.

Acceptance criteria:

• linear issues list --query <text> --json narrows results by relevant issue text such as identifier/title/description where available.
• linear issues list --updated-after <date> --json filters by issue update time.
• linear issues list --created-after <date> --json filters by issue creation time.
• linear issues list --no-parent --json filters to top-level issues.
• New filters compose with existing filters and pagination behavior.
• Help output documents supported issue list filters.
• Tests cover each new filter and at least one composed-filter case.

Out of scope:

• Server-side GraphQL optimization unless needed for correctness.
• Changing existing filter flag names.
• Parent-specific filtering beyond what is covered by the separate parent/child filtering issue.