Let the dashboard set mining cores and pause or resume mining

The Mining panel gets a cores slider (1 to the logical core count) and a pause or resume button. Applying calls miner_start(n) and saves n to <node-dir>/miner-threads, replaced atomically with its old permissions; while paused the count is only saved. Pause calls miner_stop and writes <node-dir>/mining-paused; resume removes it and starts mining on the saved count. After each change the node is read back with eth_mining and the outcome or error is shown in plain words. The new POST endpoints sit behind the dashboard key and the Origin check, and refuse a core count that is not a whole number in range. The page notes that a node restart resumes mining until the installer reads mining-paused.

Author: ghostcoin-org

README.md

@@ -37,6 +37,15 @@ The page refreshes every 5 seconds without reloading. Each panel says "Node not
 
 The dashboard finds your blocks by reading the chain over IPC and keeps what it found in `<node-dir>/dashboard-index.json` (owner-only), with the last block it read, so after a restart it only reads new blocks. On a long chain the first reading is spread over several refreshes. When the chain is reorganised it drops the blocks the new chain replaced and reads again from there; when the payout address changes it starts over.
 
+### Mining controls
+
+The Mining panel has a cores slider, from 1 to the computer's logical core count, and a pause or resume button.
+
+- **Apply** asks the node to mine on that many cores at once (`miner_start`) and saves the number in `<node-dir>/miner-threads`, the file the installer and updater read, so restarts and updates keep it. The file is replaced in one step (a temporary file renamed over it) and keeps its permissions. While mining is paused the number is only saved, and resuming uses it.
+- **Pause** stops mining (`miner_stop`) and writes `<node-dir>/mining-paused`; the node keeps syncing. **Resume** removes that file and starts mining on the saved core count. Until the node installer reads `mining-paused`, a node restart resumes mining.
+
+After each change the dashboard reads the node back (`eth_mining`) and says in plain words what happened, or what went wrong. The controls are `POST /api/mining/cores` (body `{"cores": n}`, a whole number in range, else 400), `POST /api/mining/pause` and `POST /api/mining/resume`, behind the dashboard key and the Origin check.
+
 The estimates use a target block time of 15 seconds. Each panel reads one endpoint, behind the dashboard key: `/api/node`, `/api/mining`, `/api/network`, `/api/rewards` and `/api/log`.
 
 ### Access