Persist config files across Opus package updates

The Opus package manager deletes the entire package directory on
update (fs.delete(packageDir)) before re-downloading files. This
wiped all config files (.manager_config, .client_config, etc.) that
were stored inside packages/inventory-manager/.

Fix: add _configPath() helper to every program that resolves config
file paths to usr/config/inventory-manager/ when running under Opus,
which lives outside the package directory and survives updates.
Falls back to the local _path() for standalone (non-Opus) use.

Updated files:
- inventoryManager.lua, manager/config.lua, inventoryClient.lua,
  inventoryWebBridge.lua, dropperController.lua, craftingTurtle.lua
- .package install script: saves configs to usr/config/inventory-manager/
- autorun/startup.lua: checks both persistent and package dirs
- startup/client.lua: uses persistent dir for .client_setup/.dropper_config
- web/server/Dockerfile: switch health check to wget (from prior fix)

.package

@@ -8,7 +8,8 @@
     "%.bak$", "^listDevicesByType%.lua$",
   },
   install = [[
-    local pkgDir = fs.combine("packages", "inventory-manager")
+    local cfgDir = "usr/config/inventory-manager"
+    if not fs.isDir(cfgDir) then fs.makeDir(cfgDir) end
     local function ask(prompt, default)
       if default and #default > 0 then
         write(prompt .. " [" .. default .. "]: ")
@@ -47,14 +48,14 @@
         dropperName = dropperName,
         barrelName = barrelName,
       }
-      local f = fs.open(fs.combine(pkgDir, ".manager_config"), "w")
+      local f = fs.open(fs.combine(cfgDir, ".manager_config"), "w")
       f.write(textutils.serialiseJSON(cfg))
       f.close()
       print("Saved manager config.")
 
       if serverUrl and #serverUrl > 0 then
         local bcfg = { serverUrl = serverUrl }
-        local bf = fs.open(fs.combine(pkgDir, ".webbridge_config"), "w")
+        local bf = fs.open(fs.combine(cfgDir, ".webbridge_config"), "w")
         bf.write(textutils.serialiseJSON(bcfg))
         bf.close()
         print("Saved web bridge config.")
@@ -75,7 +76,7 @@
       if dropperName and #dropperName > 0 then cfg.dropperName = dropperName end
       if barrelName and #barrelName > 0 then cfg.barrelName = barrelName end
 
-      local f = fs.open(fs.combine(pkgDir, ".client_config"), "w")
+      local f = fs.open(fs.combine(cfgDir, ".client_config"), "w")
       f.write(textutils.serialiseJSON(cfg))
       f.close()
       print("Saved client config.")
@@ -86,7 +87,7 @@
       local serverUrl = ask("Web server URL", "http://localhost")
 
       local cfg = { serverUrl = serverUrl }
-      local f = fs.open(fs.combine(pkgDir, ".webbridge_config"), "w")
+      local f = fs.open(fs.combine(cfgDir, ".webbridge_config"), "w")
       f.write(textutils.serialiseJSON(cfg))
       f.close()
       print("Saved web bridge config.")