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

web/web.go

@@ -74,6 +74,32 @@ type PlotConfiguration struct {
 	ColorScheme     []string `json:"color-scheme"`
 }
 
+const (
+	defaultImprintLink = "/imprint"
+	defaultPrivacyLink = "/privacy"
+)
+
+// FooterLink is the render-time representation of a single footer legal link.
+type FooterLink struct {
+	URL      string // Resolved target: internal path or external URL.
+	External bool   // True if the target is an external URL (opened in a new tab).
+}
+
+// FooterLinks holds the resolved legal links shown in the site footer.
+type FooterLinks struct {
+	Imprint FooterLink
+	Privacy FooterLink
+}
+
+// resolveFooterLink falls back to def when v is empty and flags external URLs.
+func resolveFooterLink(v, def string) FooterLink {
+	if v == "" {
+		v = def
+	}
+	external := strings.HasPrefix(v, "http://") || strings.HasPrefix(v, "https://")
+	return FooterLink{URL: v, External: external}
+}
+
 var UIDefaults = WebConfig{
 	JobList: JobListConfig{
 		UsePaging:     false,
@@ -266,6 +292,7 @@ type Page struct {
 	Config        map[string]any         // UI settings for the currently logged in user (e.g. line width, ...)
 	Resampling    *config.ResampleConfig // If not nil, defines resampling trigger and resolutions
 	Redirect      string                 // The originally requested URL, for intermediate login handling
+	FooterLinks   FooterLinks            // Resolved legal links for the site footer
 }
 
 func RenderTemplate(rw http.ResponseWriter, file string, page *Page) {
@@ -289,6 +316,11 @@ func RenderTemplate(rw http.ResponseWriter, file string, page *Page) {
 		}
 	}
 
+	page.FooterLinks = FooterLinks{
+		Imprint: resolveFooterLink(config.Keys.FooterLinks.Imprint, defaultImprintLink),
+		Privacy: resolveFooterLink(config.Keys.FooterLinks.Privacy, defaultPrivacyLink),
+	}
+
 	cclog.Debugf("Page config : %v\n", page.Config)
 	if err := t.Execute(rw, page); err != nil {
 		cclog.Errorf("Template error: %s", err.Error())