v0.4.5 — Stderr status output

Same code as the failed v0.4.4 (which 4xx'd in CI on a stray f-prefix), now lint-clean.

Added

[plexus] … status lines on stderr at every meaningful state change so scripts that don't configure the logging module still tell the user what's going on. Set PLEXUS_QUIET=1 to suppress.

• ✓ Connected to gateway as <source_id> on first WS auth
• ✓ Reconnected as <source_id> after a drop
• ✓ First N points landed (via ws|http) on first successful send
• ⚠ WebSocket unavailable, falling back to POST /ingest on WS failure
• ✗ Auth rejected by gateway: … / ✗ Gateway rejected the API key (401) on auth failures, with a plexus whoami hint
• ⏸ Send failed, buffering points locally (N queued) when offline
• ✓ Sending again (drained the local buffer) on recovery