feat(web): make footer legal links configurable

Add a "main.footer-links" config option so the footer Imprint and
Privacy Policy links can point at internal pages (default) or external
URLs. External http(s) targets open in a new tab; empty/unset values
fall back to the built-in /imprint and /privacy routes, keeping the
existing ./var/*.tmpl override mechanism intact.

Closes #517

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Entire-Checkpoint: c5dca72c848f

internal/config/schema.go

@@ -133,6 +133,20 @@ var configSchema = `
       },
       "required": ["subject-job-event", "subject-node-state"]
     },
+    "footer-links": {
+      "description": "Optional footer links for legal pages (imprint/privacy). Each value may be an internal path or an external URL.",
+      "type": "object",
+      "properties": {
+        "imprint": {
+          "description": "Target URL/path for the footer imprint link.",
+          "type": "string"
+        },
+        "privacy": {
+          "description": "Target URL/path for the footer privacy link.",
+          "type": "string"
+        }
+      }
+    },
     "nodestate-retention": {
       "description": "Node state retention configuration for cleaning up old node_state rows.",
       "type": "object",