feat: RAM operations run behind a blocking modal (v3.6.34)

A CAP install is a long chain of LOAD commands whose progress and results
were only visible at the bottom of a large form - and an interrupted
install can leave a half-loaded package.

- Server: _RAM_PROGRESS (+ _ram_progress_begin/step/end) records the live
  step of the running RAM operation; /api/ram-install and
  /api/ram-install-app wrap their chains in it (total = steps + 1 for the
  format check) and /api/status carries it as ram_progress - lock-free, so
  the 2 s poll works while the request holds _CARD_LOCK.
- PWA: #ram-op-modal (the STK panel pattern) blocks everything while a RAM
  operation runs: title, spinner, status line, progress bar, per-step
  result lines, Close disabled until it finishes; a beforeunload guard
  protects the window during the run.  install-cap, install-app /
  make-selectable and Explore all use the shared helpers
  (ramOpModalBegin/Status/Finish); the install results stay in the form
  area as before once the modal is closed.  The status poll feeds the modal
  via ramOpProgress (headline from the pure ramOpProgressText).
- Tests: ramOpProgressText (JS) + the progress lifecycle (Python); the
  card-state and capmem suites stub the DOM-bound hooks.
- Stylesheet rebuilt; version 3.6.34; sw simple-v307.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simple-v306';
+const CACHE = 'simple-v307';
 const URLS = [
   'index.html',
   'help.html',