docs: consolidate all docs under docs/ — single source of truth

Move issues (01–29) and PRD from .scratch/distributed-inference-network/
into docs/issues/ and docs/. Update ralph_progress.py DEFAULT_PRD path
and rewrite docs/agents/issue-tracker.md to reflect the new layout.

The distributed_inference_network.egg-info/docs/ mirror is a build
artifact already covered by *.egg-info/ in .gitignore — not committed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/issues/25-rolling-rpm-stats.md

@@ -0,0 +1,30 @@
+# US-025 — Model usage statistics: rolling RPM windows + SQLite persistence
+
+Status: done
+Priority: Medium
+Stage: Implemented
+
+## Context
+
+Trackers need per-model request-rate data to drive smart shard assignment (US-026) and
+to give operators visibility into what the network is actually serving. Stats must survive
+tracker restarts and should be shareable across a tracker cluster.
+
+## Design
+
+- `_RollingCounter`: circular-bucket counter, epoch-indexed, stale buckets auto-reset
+- Three windows: 60×1-min buckets (last hour), 24×1-hr (last day), 30×1-day (last month)
+- `_StatsCollector`: `record_request()`, `get_local_rpms()`, `merge_peer_rpms()`, `get_combined_stats()`
+- SQLite persistence via `--stats-db PATH`
+- Gossip: each tracker keeps its own slice; merge is additive (not averaged)
+
+## Acceptance criteria
+
+- [ ] `_RollingCounter` passes unit tests (record, rpm, stale bucket reset)
+- [ ] `_StatsCollector` accumulates and merges peer slices additively
+- [ ] SQLite round-trip: buckets saved and restored across restart
+- [ ] `GET /v1/stats` returns combined stats JSON
+- [ ] `POST /v1/stats/gossip` accepts peer slice and merges
+- [ ] `_handle_proxy_chat` calls `stats.record_request()` after model is resolved
+- [ ] `--stats-db PATH` CLI flag added to tracker
+- [ ] 6 unit tests pass; `python -m pytest` passes