v0.2 — Open tracker mode, configurable branding, improved tests

New features:

• OPEN_TRACKER=true env var — disables registry-only check, accepts any info_hash

Fixes:

• Fix flaky TestAnnounceCompletedEvent (background pruner race condition)

Tests:

• 24 CLI tests (up from 9), organized with shared helpers
• CLI coverage: 53.7% → 64.6%
• Total coverage: 73.7% → 74.7%

Docs:

• Document all env vars (OPEN_TRACKER, WL_TRACKER, WL_SOURCE, WL_CREATED_BY, TRACKER_SECRET) in README