📊 telemetry: restore round-level gauges on journal recovery (schema v3)

[george-connito]

The per-miner families re-emit via finalize_round_scores (which recovery replays), but validator_round_miners_{scored,pending,failed}, lifecycle_step and current_round_id are written only by the live eval workers — so after every restart the dashboard's "Evaluated N of M" column blanks for a full cycle (~1h45m) until the next Submission freeze.

Journal schema v3 adds two ints: roster_size (= len(foreground_uids) + len(background_uids), the one input Round.stats() needs that wasn't persisted) and lifecycle_step (the last live step the round reached). from_json still accepts v1/v2 (missing fields default to 0). Round now carries lifecycle_step, set alongside the gauge at the three run.py sites; the finalize journal-rewrite preserves both via the recovery stub.

On startup recovery, for each replayed journal we now also set validator_round_miners_scored/failed/pending{round_id} (pending = roster_size - scored - failed, clamped ≥0), lifecycle_step, and current_round_id (journals scan ascending, so it lands on the most recent recovered round), registering each round_id for normal eviction. Pre-v3 journals have roster_size=0 so pending clamps to 0 rather than inventing a denominator — graceful for the first restart after deploy.

Not covered (documented for the backend): validator_miner_val_loss is set at eval time and not journaled; it repopulates when miners are next evaluated. Per-miner cohort_group/assignment_role gauges likewise remain a live-only signal — M is still recoverable from the round_miners_* counters (scored+pending+failed) without them.

Tests: journal v3 round-trip, v2 back-com
pat (roster_size=0), recovery
stub carries the fields, finalize rewrite preserves them. Full telemetry

• journal suite (26) green in the stable image.