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)

startup/client.lua

@@ -2,8 +2,13 @@
 -- Auto-updates from git then launches inventoryClient + dropperController in parallel
 
 local REPO_RAW = "https://git.spatulaa.com/MayaTheShy/Inventory-Manager-CC/raw/branch/main"
-local SETUP_FILE = ".client_setup"     -- marks first-run complete
-local DROPPER_CONFIG = ".dropper_config"
+
+-- Persistent config directory (survives Opus package updates)
+local PERSIST_DIR = "usr/config/inventory-manager"
+if not fs.isDir(PERSIST_DIR) then fs.makeDir(PERSIST_DIR) end
+
+local SETUP_FILE = fs.combine(PERSIST_DIR, ".client_setup")
+local DROPPER_CONFIG = fs.combine(PERSIST_DIR, ".dropper_config")
 
 -- Files to download (destination -> repo path)
 local FILES = {