feat: query power, file input, git workflow, multi-workspace (v2026.4.16)

[aaronkwhite]

Summary

Brings the best developer-workflow ideas from schpet/linear-cli into lin, shipped across four incremental buckets:

Bucket C — Query Power

• --created-after / --updated-after date filters on issues list
• --all-teams flag for cross-team queries (conflicts with --team)

Bucket D — Content Input

• --description-file on issues create and issues update
• --body-file on issues comment

Bucket A — Developer Workflow

• issues start <ID> — fetches Linear's suggested branch name, runs git checkout -b
• issues pr <ID> — creates a GitHub PR linked to the issue (requires gh)

Bucket B — Multi-Workspace

• Named workspace config with auto-migration from legacy [auth] format
• auth login/list/default/whoami command group
• --workspace global flag (overrides default, takes priority over env var)
• Non-interactive auth login --name myco --key lin_api_... for CI/agent use

Code Review Fixes

• --workspace threaded through all 17 command execute() functions
• Explicit --workspace takes priority over LINEAR_API_KEY env var
• Date filters validate YYYY-MM-DD format before API call
• body + --body-file now errors instead of silently preferring body

Test plan

• cargo test — 116 tests pass (46 unit + 67 smoke + 3 query validation)
• cargo clippy -- -D warnings — clean
• cargo fmt --check — clean
• Verify lin issues list --all-teams --json returns cross-team results
• Verify lin issues list --created-after 2026-04-01 --json filters correctly
• Verify lin issues start <ID> --print-only returns a branch name
• Verify lin auth login --name test --key lin_api_... saves workspace
• Verify lin --workspace test auth whoami uses the correct workspace

🤖 Generated with Claude Code