fix: address v2 production UI feedback

[mambastick]

Summary

• move the background-task control into normal page flow and preserve responsive navigation spacing
• restore proxied library artwork, keep inspector copy below the hero, add per-season facts, and explain missing evidence in EN/RU
• show persisted setup completion, flatten connected-service families, and replace raw activity/status codes with user-facing summaries
• add a fail-closed single-movie Jellyfin-only deletion plan with exact-item and Radarr-absence revalidation; exclude that scope from batch deletion
• synchronize English/Russian public documentation and roadmap decisions

Fixes #16.

Safety and behavior

• the new direct flow supports one movie only
• an enabled Radarr requires a stable provider ID and a complete current catalogue with no exact or ambiguous match
• the confirmed plan is hash-bound and the Jellyfin identity/Radarr absence are checked again before execution
• the flow never mutates Arr, Seerr, or torrent-client records and remains subject to global dry-run mode
• direct Jellyfin series and batch deletion remain intentionally unavailable

Verification

• ruff format --check backend/src backend/tests
• ruff check backend/src backend/tests
• mypy backend/src
• pytest -q backend/tests — 277 passed, 7 skipped
• pnpm lint
• pnpm test — 128 passed
• pnpm build
• pnpm test:e2e — 18 passed on Chromium
• local browser walkthrough with mocked service data in light and dark themes; desktop plus automated mobile assertions, keyboard/focus checks, responsive overflow, artwork requests, season detail, and EN/RU copy

The build retains the existing Vite warning for the main chunk exceeding 500 kB. The three test-suite deprecation warnings are pre-existing.

Risk and rollback

The highest-risk change is the opt-in Jellyfin-only deletion path. Its validation, preview, queued revalidation, dry-run/live execution, malformed-catalog rejection, and batch exclusion are covered by backend and browser tests. Rollback is a revert of commit 2e47736; no migration or configuration rollback is required.

Production was not modified while preparing or verifying this PR.