feat: project overview + timeline + docs center

- services/task_project_linker.py: task<->project mapping (title keywords + workspace_path)
- routes/pages.py: /timeline, /docs, /docs/<path>, enhanced /projects/<name> and /tasks/<id>
- templates: timeline.html, docs.html, doc_view.html (new), project_detail.html + task_detail.html (overhauled)
- config.py: DOCS_DIRS + ProjectConfig color
- base.html: Timeline + Docs nav links

templates/base.html

@@ -342,6 +342,8 @@
             <a href="/">Dashboard</a>
             <a href="/projects">Projects</a>
             <a href="/tasks">Tasks</a>
+            <a href="/timeline">Timeline</a>
+            <a href="/docs">Docs</a>
         </nav>
 
         {% block content %}{% endblock %}