Add a summary report set from Markdown

from-markdown takes a hand-written summary such as SUMMARY.md and sets it
in the full report's dress: the same cover, header, footers, table of
contents, headings and grids. The shared macros move to macros.html.j2 so
both templates draw from them, and layout.render_pdf takes the template and
document title to use.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

report_generator/__main__.py

@@ -5,6 +5,7 @@ from .vendor.cc_common.config import load_environment
 from .vendor.persistent_storage.shared import inject_secrets
 
 from .commands.generate import FolderProperties, GenerateProperties, from_folder, generate
+from .commands.summary import SummaryProperties, from_markdown
 
 
 def run() -> None:
@@ -25,6 +26,12 @@ def run() -> None:
         FolderProperties,
         help="Builds the report from a folder of exported artifacts, without Postgres or the bucket.",
     )
+    cli.register_command(
+        "from-markdown",
+        from_markdown,
+        SummaryProperties,
+        help="Builds a summary report from a Markdown file, in the style of the full report.",
+    )
     cli.run()