Full reference docs, plus four fixes found writing them

[rsantacroce]

Rewrites docs/simplepool.html into a complete reference, and fixes the problems that turned up while checking it against the source.

Needs operator action

• Dashboard now listens on loopback by default (DASHBOARD_BIND=127.0.0.1). Nothing changes behind nginx. A server that serves the dashboard directly on :8081 needs Environment=DASHBOARD_BIND=0.0.0.0 in its systemd drop-in before it is upgraded or redeployed. deploy-to-server.sh re-renders the unit from the template, so without that line the dashboard stops answering on :8081. install.sh sets the right value itself (loopback with nginx, 0.0.0.0 with --no-nginx), and the Docker image sets 0.0.0.0 inside the container.

Changes miner payouts

• pplns-thunder / pplns-btc: a fee under the dust limit is no longer deducted. When a block's fee_bps came to less than 546 sats, the coinbase had no fee output, so the pool wallet received the whole reward. The distributor still took fee_bps off before crediting miners, so the difference stayed in the pool wallet, credited to no one. It now applies the coinbase's dust rule. This only affects blocks under about 546 × 10000 / fee_bps sats (54,600 at 1%).

Fixes

• An eighth listener line is now a config error. listen_port takes one of the eight port slots, so only seven extra ports can be bound. An eighth used to load without error and then silently not be bound.
• install.sh --help no longer says --pps-sats-per-diff defaults to 1000; it defaults to unset, so the rate is derived per template. The installer also warns when the flag is passed.
• schema.sql documents why the unique blocks_found(hash) index is created by the proxy at startup and not in this file. It also fixes the events_lost comment, which called a counter unix seconds.

Docs

docs/simplepool.html now covers everything below, all checked against the source:

• every proxy.conf key with its default, allowed values and failure behaviour; the listener sub-keys; what each mode requires; removed keys; command-line flags and exit codes
• every environment variable for the payout, dashboard and slipstream services
• the stratum protocol as implemented: methods, notifications, the order submits are checked in, error codes, username rules, d=<n>, vardiff
• the coinbase layout, byte by byte and per mode
• ports, all HTTP APIs, Redis channels and upstream RPC calls
• the full database schema and how a block's status moves
• hard limits, and build/release/tests

It also corrects stale claims: extranonce1 is no longer XORed with the clock, the stratum password is read for d=<n>, the stat card now says five modes, and a CSS fix stops the page scrolling sideways on phones. The generated sequence diagrams are unchanged, and sequence-diagrams.py --check passes.

CHANGELOG.md has an Unreleased section with the two call-outs above.

Testing

• make test: all 11 C suites pass. New tests:
  • test_config: 7 listeners load, 8 are refused
  • test_store: a dust-sized fee is not deducted (fails on the old code), and a real fee still is
• npm test in dashboard/: 189 pass, 2 skipped
• Started the dashboard with and without DASHBOARD_BIND and checked with lsof that it listens on 127.0.0.1 by default and on * with DASHBOARD_BIND=0.0.0.0.
• Checked the page at desktop and phone widths: no sideways scrolling at 390px, and every internal link resolves.