refactor: count every run line from one tally

The run header, the menu, its game data split and g, the plan, the
screen's plan and game data row and both results now divide one tally
of the list the run keeps. Case variants were counted on the run and
missing from the screen's split, g counted the whole list under a head
narrowed by c, and the result left out the data tree files. The wiki
examples come from real runs of 2026-10-27.

wiki/installer.md

@@ -307,17 +307,22 @@ names `~/Emulation/saves/retroarch/saves`. RetroPie, ROCKNIX, AmberELEC and
 EmuELEC keep saves beside each game, and RomM keeps them in the browser: their
 lists record these files as omitted.
 
-A RetroArch run into an empty folder printed this on 2026-10-21:
+A RetroArch dry run into an empty folder printed this on 2026-10-27:
 
 ```
 Fetching file index for retroarch...
-  8069 files (6.5 GB)
-  Not installable: 11 files (1 required, not found: 11).
+  106 files read from RetroArch's save directory go to a folder per core under /home/me/.config/retroarch/saves
+  8358 files (6.6 GB)
+    3269 BIOS files (4.1 GB) and 5089 game data files (2.5 GB).
+  Not installable: 37 files (1 required, not found: 37).
 
 Checking existing files...
-  0/8069 present (0 verified, 0 wrong hash)
+  0/8358 present (0 verified, 0 wrong hash)
 ```
 
+The second line divides the first, and every later count of the run (the
+menu, the plan, `--dry-run`, the result) is taken from the same list.
+
 When the manifest leaves entries out (a file the collection cannot supply, or
 one that failed its hash check), a `Not installable:` line under the index count
 says how many and why. `--check` and the closing report also name the required
@@ -615,25 +620,28 @@ By default the installer fetches everything the platform runs. At a terminal,
 the plan screen of the [full-screen interface](#the-full-screen-interface)
 offers **Install**, **Choose systems** and **Options**. With `--plain`, or where
 the full screen cannot open (a terminal smaller than 40x12, `TERM=dumb`), the
-same choice comes as questions after detection:
+same choice comes as questions after detection. A RetroArch run with `--plain`
+printed this on 2026-10-27:
 
 ```
-RetroArch: 8348 files, 7.1 GB.
-  3259 BIOS files (4.4 GB) and 5089 game data files (2.7 GB).
+RetroArch: 8358 files, 6.6 GB, and 2636 data files (38.5 MB).
+  3269 BIOS files (4.1 GB) and 5089 game data files (2.5 GB).
   BIOS folder: /home/me/.config/retroarch/system
+  106 files read from RetroArch's save directory go to a folder per core under /home/me/.config/retroarch/saves
   Enter) install everything
-  i) only what the installed cores read: 100 files, 44.2 MB
+  i) only what the installed cores read: 87 files, 43.8 MB
   c) choose systems, cores and regions
   f) copy from a folder or an old card
-  g) leave out the 5089 game data files (2.7 GB), game data: files a game or a game engine reads, of no use to the other cores
+  g) leave out the 5089 game data files (2.5 GB), game data: files a game or a game engine reads, of no use to the other cores
   q) quit
 ```
 
 A list that marks its game data counts it apart from the BIOS files, on the
-plan, in this menu and on the result (`Installed: 3259 BIOS files and 5089 game
-data files.`). `g` leaves it out, as `--no-game-data` does, and counts again
+plan, in this menu and on the result (`Installed: 3269 BIOS files, 5089 game
+data files and 2636 data files.`), the parts adding up to the total. `g` leaves
+the game data of the choice out, as `--no-game-data` does, and counts again
 (`g` then keeps it). The plan screen has the same choice as a row of its own,
-**Game data (5089 files, 2.7 GB): kept, leave out**, one press toggling it,
+**Game data (5089 files, 2.5 GB): kept, leave out**, one press toggling it,
 and Options keeps its **Game data** row too.
 
 `i` appears for RetroArch, Lakka and RetroPie when cores are found installed,