Finalize MDFC follow-ups, docs, and diagnostics tooling

document deck summary DFC badges, exporter annotations, and per-face metadata across README/DOCKER/release notes

record completion of all MDFC roadmap follow-ups and add the authoring guide for multi-face CSV entries

wire in optional DFC_PER_FACE_SNAPSHOT env support, exporter regression tests, and diagnostics updates noted in the changelog

code/deck_builder/shared_copy.py

@@ -0,0 +1,30 @@
+"""Shared text helpers to keep CLI and web copy in sync."""
+
+from __future__ import annotations
+
+from typing import Optional
+
+__all__ = ["build_land_headline", "dfc_card_note"]
+
+
+def build_land_headline(traditional: int, dfc_bonus: int, with_dfc: Optional[int] = None) -> str:
+    """Return the consistent land summary headline.
+
+    Args:
+        traditional: Count of traditional land slots.
+        dfc_bonus: Number of MDFC lands counted as additional slots.
+        with_dfc: Optional total including MDFC lands. If omitted, the sum of
+            ``traditional`` and ``dfc_bonus`` is used.
+    """
+    base = max(int(traditional), 0)
+    bonus = max(int(dfc_bonus), 0)
+    total = int(with_dfc) if with_dfc is not None else base + bonus
+    headline = f"Lands: {base}"
+    if bonus:
+        headline += f" ({total} with DFC)"
+    return headline
+
+
+def dfc_card_note(counts_as_extra: bool) -> str:
+    """Return the descriptive note for an MDFC land entry."""
+    return "Adds extra land slot" if counts_as_extra else "Counts as land slot"