ci(docs): auto-sync PROJECT_TREE.md to the docs repo on push to main

Add a sync-project-tree workflow that regenerates this repo's tracked-file
tree and opens (or force-updates) a PR against RunicGateway/docs whenever the
layout on main changes. Never writes to the docs repo's main directly. Reuses
the existing REGISTRY_USER / REGISTRY_TOKEN secrets. Tree rendering lives in
.gitea/scripts/gen_tree.py (deterministic, dirs-first ordering).

Co-Authored-By: Claude <noreply@anthropic.com>

.gitea/scripts/gen_tree.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+"""Render an ASCII tree of tracked files, read from stdin (one path per line).
+
+Used by the `sync-project-tree` workflow to regenerate this repo's PROJECT_TREE.md
+snapshot in the RunicGateway/docs repo. Feed it `git ls-files`:
+
+    git ls-files | python3 .gitea/scripts/gen_tree.py <root-label>
+
+Deterministic ordering: directories before files, each group sorted
+case-insensitively with the raw name as a tiebreak. Output uses the classic
+`tree(1)` box-drawing style so the result is stable across runs and platforms.
+"""
+import sys
+
+
+def build(paths):
+    root = {}
+    for p in paths:
+        p = p.strip().replace("\\", "/")
+        if not p:
+            continue
+        node = root
+        for part in p.split("/"):
+            node = node.setdefault(part, {})
+    return root
+
+
+def render(node, prefix, lines):
+    entries = list(node.items())
+    # directories (non-empty children dict) before files, then case-insensitive name
+    entries.sort(key=lambda kv: (0 if kv[1] else 1, kv[0].lower(), kv[0]))
+    for i, (name, child) in enumerate(entries):
+        last = i == len(entries) - 1
+        branch = "└── " if last else "├── "
+        suffix = "/" if child else ""
+        lines.append(f"{prefix}{branch}{name}{suffix}")
+        if child:
+            render(child, prefix + ("    " if last else "│   "), lines)
+
+
+def main():
+    try:
+        sys.stdout.reconfigure(encoding="utf-8", newline="\n")
+    except AttributeError:
+        pass
+    root_label = sys.argv[1] if len(sys.argv) > 1 else "."
+    tree = build(sys.stdin.read().splitlines())
+    lines = [f"{root_label}/"]
+    render(tree, "", lines)
+    sys.stdout.write("\n".join(lines) + "\n")
+
+
+if __name__ == "__main__":
+    main()