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)

inventoryClient.lua

@@ -30,6 +30,16 @@ local DROPPER_ANNOUNCE_INTERVAL = 30  -- seconds between dropper announcements
 local _baseDir = fs.getDir(shell.getRunningProgram())
 local function _path(rel) return fs.combine(_baseDir, rel) end
 
+-- Persistent config path: survives Opus package updates
+local _PERSIST_DIR = "usr/config/inventory-manager"
+local function _configPath(rel)
+    if fs.isDir(_PERSIST_DIR) or fs.isDir("packages/inventory-manager") then
+        if not fs.isDir(_PERSIST_DIR) then fs.makeDir(_PERSIST_DIR) end
+        return fs.combine(_PERSIST_DIR, rel)
+    end
+    return _path(rel)
+end
+
 -- Override dofile to load modules into our _ENV so they inherit
 -- Opus's require/package (CC:Tweaked dofile uses _G instead).
 local _ccDofile = dofile
@@ -39,7 +49,7 @@ local function dofile(path)                     -- luacheck: ignore
     else error(err, 2) end
 end
 
-local CLIENT_CONFIG_FILE = _path(".client_config")
+local CLIENT_CONFIG_FILE = _configPath(".client_config")
 
 -------------------------------------------------
 -- Modules