Mark native-backed tasks on card, sidebar and breadcrumb

[h0x91b]

One shared, non-interactive marker states a task's persisted terminal-backend identity next to its title on all three task-identity surfaces: the Kanban card, the Active Tasks sidebar row, and the Task View breadcrumb.

• New NativeBackendMark component (plus isNativeBackendTask) derives the identity through the shared terminal-backend-identity codec — explicit native only. Explicit tmux, legacy unmarked records, and any unknown value render nothing.
• The marker means stored identity only; it says nothing about whether a terminal is running, connected or healthy. Tooltip and aria-label in en/ru/es say so.
• No schema, persistence, migration, backfill or backend-switching change.

Live browser QA on the real board (dark + light, 1440px and 560/760px narrow): marker present on native tasks in all three surfaces, absent on tmux/legacy, no console errors.

Supersedes #1232, which GitHub closed automatically when its opaque head branch was renamed to satisfy the repository branch-naming rule.