generate-docs-sections.ts: project-structure tree rendering invariant

In generateProjectStructure() (line 178 comment): groups (route directories) always use ├── prefix regardless of position — because standalones always follow groups. Standalone entries include help.ts (added manually before sort); last standalone uses └──, others use ├──. Both groups and standalones sorted alphabetically within their sections. Output is a fenced code block with cli/ tree.