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/20-tracker-node-hardening.md

@@ -0,0 +1,20 @@
+# US-020 — Tracker + node hardening: BrokenPipe fix, deterministic node IDs, HF coverage
+
+Status: done
+Priority: High
+Stage: Maintenance
+
+## Context
+
+First two-machine LAN test (US-018) exposed three reliability issues:
+
+1. `BrokenPipeError` crash in tracker `_send_json` when a slow-inference client disconnected mid-response
+2. Random UUID node IDs meant every re-registration (after tracker restart) created a phantom entry
+3. `GET /v1/coverage/<model>` returned no results when called with a short name (`Qwen2.5-0.5B`) instead of the full HF repo ID
+
+## Acceptance criteria
+
+- [ ] `BrokenPipeError` in tracker and node `_send_json` is silently swallowed
+- [ ] Node IDs are deterministic: `sha256(wallet_address + str(port))[:16]`
+- [ ] `GET /v1/coverage/<model>` accepts both short names and full `owner/repo` IDs
+- [ ] `python -m pytest` passes from repo root