Show feed-published release stats on Find Mods rows

A mod index can now publish three optional per-entry fields -- downloads
(total across every release), first_release and last_release (ISO days) --
which the FIND MODS listing shows in the same gold line the MODS tab uses.

The fields are additive by design: feeds that carry them stay readable by
every build that predates them (schema_version stays 1), and feeds that do
not render exactly as before. ModUpdate.statsLine builds the shared line;
the MODS tab reuses it. Parser, formatting, and parse coverage are tested.

src/mods/ModUpdate.lua

@@ -7,6 +7,8 @@ local ModUpdate = {}
 
 ModUpdate.CACHE_TTL = 6 * 60 * 60  -- six hours
 
+local Strings = require("src.core.Strings")
+
 local function stripV(tag)
   return (tostring(tag):gsub("^[vV]", ""))
 end
@@ -237,6 +239,24 @@ function ModUpdate.formatCount(n)
   return (s:gsub("^,", ""))
 end
 
+-- The one-line stats string both launcher panels show: "1,234 downloads
+-- across all releases  -  Released 2024-05-31  -  Updated 2026-07-01".
+-- Each part is optional; nil everywhere means nil, so a row with no data
+-- shows no line rather than a wrong "0".
+function ModUpdate.statsLine(total, first, latest)
+  local parts = {}
+  if total ~= nil then
+    parts[#parts + 1] = Strings("%s downloads across all releases",
+      ModUpdate.formatCount(total))
+  end
+  if first or latest then
+    parts[#parts + 1] = Strings("Released %s  -  Updated %s",
+      first or "?", latest or "?")
+  end
+  if #parts == 0 then return nil end
+  return table.concat(parts, "  -  ")
+end
+
 -- ------- cache (options.modUpdateCache[repo])
 
 local function cacheStore()