feat(game): race exit warnings in the turn report (#12)

Surface the inactivity-removal countdown the rules promise but the
engine never reported. A race within five turns of being auto-removed
for inactivity gets a personal warning in its own report; every race
within three turns is listed publicly to all participants.

- model: Report.PersonalExitWarning + RacesLeavingSoon ([]RaceExitNotice)
- fbs: RaceExitNotice table + Report.personal_exit_warning /
  races_leaving_soon (regenerated Go + TS bindings)
- transcoder: encode/decode both fields
- engine: ReportExitWarnings fills the recipient's TTL (1..5) and lists
  other non-extinct races with TTL 1..3, excluding the recipient itself
- ui: danger-styled personal banner + "races leaving soon" section
  (hidden when empty), wired into the report view, EN/RU i18n
- docs: rules.txt report-section list, FUNCTIONAL.md 6.4 + RU mirror

Voluntary quit and idle timeout share the TTL countdown and are not
distinguished, per the agreed scope.

docs/FUNCTIONAL.md

@@ -704,11 +704,18 @@ demand. Backend authorises the caller and forwards the request;
 there is no caching or denormalisation in this path.
 
 The web client renders the report as one section per FBS array
-(galaxy summary, votes, player status, my / foreign sciences, my /
-foreign ship classes, battles, bombings, approaching groups, my /
-foreign / uninhabited / unknown planets, ships in production,
-cargo routes, my fleets, my / foreign / unidentified ship groups).
-Empty sections render explicit empty-state copy. Section
+(galaxy summary, races leaving soon, votes, player status, my /
+foreign sciences, my / foreign ship classes, battles, bombings,
+approaching groups, my / foreign / uninhabited / unknown planets,
+ships in production, cargo routes, my fleets, my / foreign /
+unidentified ship groups). Empty sections render explicit
+empty-state copy; "races leaving soon" is the exception and hides
+entirely when no race is near removal. When the local race is
+itself within five turns of being auto-removed for inactivity, a
+danger-styled personal warning banner above the section list
+carries its own turns-remaining countdown; the public "races
+leaving soon" section lists every other race within three turns
+of removal. Section
 navigation is exposed through a sticky icon-popup menu pinned to
 the top-right of the report column (an anchored popover on desktop
 and a fixed bottom-sheet on mobile); the trigger label tracks the