Logs: every log in app-private storage, shared as one scrubbed zip (#484)

Session folders, tool and installer logs and the stores' log now all live under the
app's private files/logs instead of Download/DroidDeck, and every existing "Share
logs" action bundles them into one zip that goes through a final scrub.

- Where: LinuxRuntime.logDir() = files/logs; sessions keep their dated folders and
  30-session pruning, tools/ and stores/ beside them. The "Logs" setting keeps its
  meaning. Game save backups stay in Download/DroidDeck/Saves.
- Migration: at first start the old session folders, tools/ and loose logs move from
  Download/DroidDeck into files/logs (Saves untouched), and every moved folder is
  scrubbed under the current rules.
- Scrubbing: one rule set (SecretScrub) for the stores' log and the zip. The scrub
  marker carries the rules version, so a rules change re-scrubs every folder at the
  next start (in the background, a few at a time). Steam login account names and
  emails, account-name fields, OAuth codes, tokens in URLs and private LAN
  addresses are removed; Windows exception codes and server addresses are kept.
- Share: one zip of the current session folder plus the last 7 days of stores/ and
  tools/, written to cache/share and handed to the share sheet.

docs/development/flatpak.md

@@ -22,7 +22,7 @@ The script then unpacks them without hooks and checks what the binaries link. Li
 the Desktop package normally brings (PyGObject, json-glib, fuse3 and others) are fetched too,
 but only when their files are missing. Flathub is added as a per-user remote from a copy of
 its `.flatpakrepo` carried in the script, so that step needs no network. Every store command
-writes its output to `Download/DroidDeck/flatpak-<verb>.log`, next to the session logs. The
+writes its output to `files/logs/tools/flatpak-<verb>.log`, next to the session logs. The
 setup script also puts Flatpak's own error text in the failure message the app shows.
 
 ## bubblewrap without namespaces