fix(bootstrap): harden archive names, the cancel window and quit wait

The bootstrap preflight's protected names could be bypassed by names
that resolve onto them, and its cancel and quit paths had two timing
gaps.

- Entry names are judged as the file system resolves them: '\' is a
  separator, "." components are dropped and each component loses its
  trailing dots and spaces, as Win32 does ("./wallet.dat" and
  "DRAGONX.conf." name protected files). The whole archive is refused
  for an absolute or drive-rooted name, a ".." component, any ':'
  (drive letter or NTFS alternate data stream, "DRAGONX.conf::$DATA"),
  an 8.3 short name ("DRAGON~1.CON"), a component of only dots or
  spaces (other than "."), and any byte >= 0x80 or ASCII control
  character: macOS folds or ignores some Unicode (U+017F, U+212A,
  U+200C) onto a protected name, and the published bootstrap archive
  uses plain ASCII names. A refused name is echoed
  with \xNN escapes. A member is written at the path it was checked
  under, and the protected-name check runs on the resolved name.
- The user's Cancel (Settings dialog and first-run wizard) goes through
  requestCancel(). It is refused once the old chain data starts being
  replaced, and the start of that window re-checks a cancel under the
  same lock, so a click lands before the old chain is touched or not at
  all.
- Quit cancels the wizard's and the Settings bootstrap when the
  shutdown starts; the HEAD and checksum requests now end at once on
  cancel, and a cancelled HEAD keeps the partial download. A run
  cancelled before the window leaves the old chain as it was. A run
  inside it stops extracting and removes its partial chain while the
  shutdown screen shows "Cleaning up...", so it ends with no chain data
  (wallet.dat untouched; Retry reuses the zip, or the node resyncs).
  That wait is bounded: at most 2 minutes from the start of the
  shutdown, then 3 s in shutdown(), after which a worker still running
  is left to the process exit. Only a cleanup that overruns that cap
  can leave a partial chain, which dragonxd then answers with its
  reindex offer.

Tests: refusal of the Windows-resolved, non-ASCII and control-character
names with the escaped echo; the protected-name list incl. the resolved
forms and a planted -wallet file, conf and database/ that stay
byte-identical; the user-cancel window; the bounded quit wait and
safeToAbandon(); a cancel ends a HEAD request that never answers.

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

src/app.h

@@ -180,9 +180,16 @@ public:
     bool shouldQuit() const {
         if (!quit_requested_ || !shutdown_complete_) return false;
         auto elapsed = std::chrono::steady_clock::now() - shutdown_start_time_;
-        return elapsed >= std::chrono::seconds(1);
+        return elapsed >= std::chrono::seconds(1) && !bootstrapQuitPending();
     }
 
+    /**
+     * @brief A bootstrap cancelled by beginShutdown() is still replacing the chain data (its abort removes the
+     * partial chain). The shutdown screen stays up until it is done (capped), so main()'s exit watchdog never
+     * cuts it off.
+     */
+    bool bootstrapQuitPending() const;
+
     /**
      * @brief Request application exit — begins async shutdown
      */