Add mining turtle for infinite cobblestone generators

New miningTurtle.lua: sits on top of a cobble gen, continuously
digs down, and pushes items into networked chests via wired modem.
Features:
- Configurable mine interval, dump threshold, fuel slot
- Auto-dumps inventory when slots fill or timer expires
- Auto-refuels from designated fuel slot
- Remote reboot via SYSTEM_CHANNEL
- Stats display (mined, dumped, uptime, fuel)
- Persistent config in usr/config/inventory-manager/.miner_config

Also adds:
- startup/miner.lua: auto-update + launch script for standalone use
- .package: new 'Mining Turtle' role (option 4) in setup wizard
- autorun/startup.lua: detects .miner_config and launches miningTurtle

.package

@@ -28,9 +28,10 @@
     print("  1) Inventory Manager (main controller)")
     print("  2) Inventory Client  (display-only)")
     print("  3) Web Bridge        (HTTP forwarder)")
-    print("  4) Skip setup")
+    print("  4) Mining Turtle     (cobble miner)")
+    print("  5) Skip setup")
     print("")
-    write("Choice (1/2/3/4): ")
+    write("Choice (1/2/3/4/5): ")
     local choice = read()
 
     if choice == "1" then
@@ -92,6 +93,21 @@
       f.close()
       print("Saved web bridge config.")
 
+    elseif choice == "4" then
+      print("")
+      print("-- Mining Turtle Configuration --")
+      local mineInterval = ask("Mine interval in seconds", "0.5")
+      local dumpThreshold = ask("Dump when N slots full", "14")
+
+      local cfg = {
+        mineInterval = tonumber(mineInterval) or 0.5,
+        dumpThreshold = tonumber(dumpThreshold) or 14,
+      }
+      local f = fs.open(fs.combine(cfgDir, ".miner_config"), "w")
+      f.write(textutils.serialiseJSON(cfg))
+      f.close()
+      print("Saved miner config.")
+
     else
       print("Skipped — edit config files manually later.")
     end