fix(diagnostics): deep-review round 3 — a keyboard owner that is not a Tab trap

Round 2 made the step prompt a blocking layer so that `j` and the `g` chords
would not reach the page behind it. The dialog it sits in gave up its Tab trap
because of that, while the prompt's own replacement trap covered only its own
two controls — so Tab from anywhere else in the dialog (the bar's Screenshot or
Stop, the dialog's own buttons) walked out behind the scrim. `layerStack` now
separates the two questions it had folded into one flag: a layer can own the
keyboard and still leave the Tab trap to the dialog below it. The mirror case,
a dialog opening over the prompt, falls out of the same split.

A send's claim is now a lease with an owner. Every progress report re-stamps
it, so a send slower than the lease cannot lose it while it is still running,
and only the send that took a claim can give it back. The issue_create audit
row is staged inside the send and rides the same checkpoint as `issue_url`, so
the trail cannot be missing for an issue that exists. The attachment-name
prefix has one definition, shared by the producer and both readers.

A running send is reported to the UI. A reload or a second tab used to render
it exactly like a send that STOPPED, and offered a retry the server was certain
to refuse; the composer now says the report is being sent, holds the draft, and
puts both the retry and Create issue out. The past-sessions list says the same
for the same reason — it is the list a user opens to check on a send, and both
"draft" and "half sent" describe one that died. `/preview` and the retry path
got a pace of their own, and the per-user byte cap took the user-scoped lock
that makes it a cap instead of a guess.

Verified in a real browser on localdev: Tab cycles the whole dialog with the
prompt open, the prompt still swallows the page's keys, and the issue link is
focusable where the composer puts it. All 24 regression tests mutation-checked.

frontend/src/i18n/locales/en/errors.json

@@ -226,6 +226,8 @@
     "debug_session_rate_limited": "You can start at most {{limit}} new recordings an hour. Try again later.",
     "export_rate_limited": "Too many downloads in a row. Wait a minute.",
     "screenshot_storage_full": "You've reached the {{limit}} MB screenshot allowance. Remove images from older sessions, or wait until they expire.",
-    "issue_sending": "The report is being sent right now. Wait for it to finish."
+    "issue_sending": "The report is being sent right now. Wait for it to finish.",
+    "issue_rate_limited": "At most {{limit}} send attempts an hour. Try again later.",
+    "preview_rate_limited": "Too many previews in a row. Wait a minute."
   }
 }

frontend/src/i18n/locales/en/recorder.json

@@ -109,6 +109,8 @@
     "shotsFailed": "Couldn't load the screenshots",
     "removeShotFailed": "Couldn't remove the screenshot",
     "partialImages": "The issue was created, but its text does not show the screenshots yet.",
+    "retryImages": "Show them in the issue",
+    "sendingNow": "The report is being sent…",
     "exportFailed": "Couldn't build the zip"
   },
   "issue": {
@@ -128,6 +130,8 @@
     "empty": "No session recorded yet.",
     "open": "Open",
     "sent": "Sent",
+    "partial": "Half sent",
+    "sending": "Sending",
     "draft": "Draft",
     "unwritten": "Not written yet",
     "failed": "Couldn't load the sessions"

frontend/src/i18n/locales/hu/errors.json

@@ -226,6 +226,8 @@
     "debug_session_rate_limited": "Óránként legfeljebb {{limit}} új rögzítést indíthatsz. Próbáld újra később.",
     "export_rate_limited": "Túl sok letöltés egymás után. Várj egy percet.",
     "screenshot_storage_full": "Elérted a képernyőképek {{limit}} MB-os keretét. Törölj régebbi munkamenetekből képeket, vagy várd meg, amíg lejárnak.",
-    "issue_sending": "A hibajegy küldése épp folyamatban van. Várd meg, amíg befejeződik."
+    "issue_sending": "A hibajegy küldése épp folyamatban van. Várd meg, amíg befejeződik.",
+    "issue_rate_limited": "Óránként legfeljebb {{limit}} küldési kísérlet. Próbáld újra később.",
+    "preview_rate_limited": "Túl sok előnézet egymás után. Várj egy percet."
   }
 }

frontend/src/i18n/locales/hu/recorder.json

@@ -109,6 +109,8 @@
     "shotsFailed": "Nem sikerült betölteni a képernyőképeket",
     "removeShotFailed": "Nem sikerült törölni a képernyőképet",
     "partialImages": "A hibajegy létrejött, de a képernyőképek még nem látszanak a szövegében.",
+    "retryImages": "Megjelenítés a hibajegyben",
+    "sendingNow": "A hibajegy küldése folyamatban…",
     "exportFailed": "Nem sikerült elkészíteni a zipet"
   },
   "issue": {
@@ -128,6 +130,8 @@
     "empty": "Még nincs rögzített munkamenet.",
     "open": "Megnyitás",
     "sent": "Elküldve",
+    "partial": "Félig elküldve",
+    "sending": "Küldés alatt",
     "draft": "Vázlat",
     "unwritten": "Megírásra vár",
     "failed": "Nem sikerült betölteni a munkameneteket"