fix: SCP80/RAM re-read the preset before every operation; no counter bump on a rejected send (v3.6.3)

The SCP80/RAM forms hold a copy of the preset (counter, keys, TAR, SPI).
Editing the preset on the Cards tab saved correctly, but the form kept the
old copy: the operation sent the stale counter (the card answers cntr_low)
and the post-send sync wrote the stale value back over the preset - the
saved counter silently reverted.  Reproduced in a real DOM:

  after select in SCP80:  preset=0000000001  sp=0000000001
  after Cards edit+save:  preset=00000000AA  sp=0000000001
  after a sync:           preset=0000000001  (edit lost)

- `cardsApply()` split into `cardsApplyFields()` (field copy, no packet) and
  `cardsApply()` = fields + genSp; new `spRefreshFromPreset(selId)` re-reads
  the selected preset from `sp-card-sel` / `ram-card-sel` and re-applies it.
- `pysimSendOta()` and `ramExecute()` call it before starting, so every
  SCP80/RAM operation uses the preset as it is now.
- A rejected send no longer advances the counter: new `spPorAccepted(por)`
  gates the advance+write-back in `pysimSendOta`, the Explore pagination and
  its GET DATA step, and the server's RAM install (`_ram_next_cntr`: advance
  only for `por_ok`/`no_por` steps).  A failed install still returns
  `final_cntr` (the accepted prefix) and the PWA persists it, so a retry
  never replays a counter the card already consumed.
- tests: cards_counter.test.js (the stale-form regression, RAM selector,
  fields-without-genSp, spPorAccepted) and `_ram_next_cntr` cases; the
  cards_form/ram harnesses updated for the split.
- docs/api.md counter semantics; AGENTS preset-source-of-truth rule.

607 frontend / 488 Python green; version 3.6.3; sw simple-v276.

tests/test_ota_helpers.py

@@ -31,6 +31,7 @@ from pysim_simple_server.server import (
     _parse_select_item,
     _parse_setup_menu_items,
     _por_remote_sw,
+    _ram_next_cntr,
     _ram_remote_sw_ok,
     _ram_step_result,
     _record_tr,
@@ -1300,6 +1301,11 @@ class RamPorStepTest(unittest.TestCase):
         self.assertEqual(err, 'PoR undecodable')
         self.assertEqual(step['por_raw'], 'DEADBEEF')
 
+    def test_counter_advances_only_for_accepted_packets(self):
+        self.assertEqual(_ram_next_cntr('0000000010', True), '0000000011')
+        self.assertEqual(_ram_next_cntr('0000000010', False), '0000000010')
+        self.assertEqual(_ram_next_cntr('FFFFFFFF', True), '0000000000')
+
     def test_remote_sw_from_expanded_response(self):
         por = {'response_status': 'por_ok', 'decoded': {},
                'responses': [{'status_word': '9000'}, {'status_word': '6A82'}]}