generate subpage listings automatically

right now very barebones!

- doesn't sort pages quite correctly
- no search function
- still not sure about the UI design aspects

includes refactor of tree generation code

static/css/tree.css

@@ -326,7 +326,7 @@ th-bd {
 
 /* Hide branch dates on very small displays. No clue how to fix this just yet. */
 @media (max-width: 600px) {
-    th-bb .branch-date {
+    th-bd {
         display: none;
     }
 }
@@ -397,6 +397,23 @@ th-bd {
     opacity: 80%;
 }
 
+/* Children containers */
+
+.tree li.child-pages {
+    margin-top: 0.8rem;
+    padding-top: 0.8rem;
+    padding-bottom: 0.8rem;
+    border-top: 0.1rem solid var(--border-1);
+
+    & > ul {
+        /* Show child page lists without an indent.
+           Visually they belong to the root of the page. */
+        margin-left: 0;
+        padding-left: 0;
+        border-left: none;
+    }
+}
+
 /* branch-quote class for "air quote branches"; used to separate a subtree from a parent tree
    stylistically such that it's interpretable as a form of block quote. */
 ul.branch-quote {

static/js/tree.js

@@ -73,9 +73,14 @@ export class Branch {
             });
         }
 
-        if (ulid.isCanonicalUlid(this.namedID)) {
-            // Adjust dates to fit the user's time zone.
-            let timestamp = ulid.getTimestamp(this.namedID);
+        // Adjust dates to fit the user's time zone.
+        let timestamp = null;
+        if (element.hasAttribute("th-ts")) {
+            timestamp = new Date(parseInt(element.getAttribute("th-ts")));
+        } else if (ulid.isCanonicalUlid(this.namedID)) {
+            timestamp = ulid.getTimestamp(this.namedID);
+        }
+        if (timestamp != null) {
             let branchDate = this.buttonBar.getElementsByTagName("th-bd")[0];
             branchDate.textContent = dateToString(timestamp);
         }