Refactor nginx to path-based domain model with config migration

Replace the legacy top-level management key with a unified paths-based
model. Each domain now contains a paths map where each entry defines its
own backend, auth, headers, and flags (is_management, is_websocket).

- Add _migrate_config() to auto-migrate legacy formats on first load
- Remove set_management_proxy() and POST_NGINX_MANAGEMENT endpoint
- Update server_block.conf template to iterate paths with per-location auth
- Update daemon handler, API blueprint, state collector, and install script
- Add server config generation tests for paths, WebSocket, auth inheritance
- Update frontend proxy page to display per-path rows with flags

lib/state.py

@@ -636,7 +636,6 @@ def _collect_nginx() -> dict[str, Any]:
 
     default_cfg: dict[str, Any] = {
         "domains": {},
-        "management": None,
         "ssl": deepcopy(DEFAULT_SSL),
     }
     cfg = deepcopy(default_cfg)
@@ -652,18 +651,27 @@ def _collect_nginx() -> dict[str, Any]:
         except Exception:
             pass
 
-    # Build domains list with site existence
+    # Build flattened domains list (one entry per path)
     domains: list[dict[str, Any]] = []
     for name, dom in cfg.get("domains", {}).items():
         site = SITES_DIR / f"{name}.conf"
-        domains.append(
-            {
+        paths = dom.get("paths", {})
+        if not paths:
+            continue
+        for ppath, pcfg in paths.items():
+            entry: dict[str, Any] = {
                 "domain": name,
-                "backend": dom.get("backend", {}),
+                "path": ppath,
+                "backend": pcfg.get("backend", {}),
                 "online": site.exists() if SITES_DIR.exists() else False,
                 "force_ssl": dom.get("force_ssl", True),
+                "cert": dom.get("cert"),
             }
-        )
+            if pcfg.get("is_management"):
+                entry["is_management"] = True
+            if pcfg.get("is_websocket"):
+                entry["is_websocket"] = True
+            domains.append(entry)
 
     return {
         "config": cfg,
@@ -819,7 +827,8 @@ def _collect_acme() -> dict[str, Any]:
             if not main:
                 continue
             san_domains = [
-                d.strip() for d in entry.get("san_domains", "").split(",")
+                d.strip()
+                for d in entry.get("san_domains", "").split(",")
                 if d.strip() and d.strip().lower() != "no"
             ]
             cert_dir = acme_home / main