View-tag scanning strategy toggle

[truthixify]

Tier: S (1-2 days) | Type: ux

Context. The receive scanner runs a fixed strategy today. Power users on slow links want a fast "view-tag only" pass; auditors want a full scan that ignores the tag entirely. Expose the choice with copy that explains the privacy tradeoff instead of hiding it behind a flag.

Scope.

• Settings section "Scanning strategy" with three radios: Fast (view-tag), Balanced (default), Full (ignore tag).
• Persist to the existing settings surface; the scanner worker reads it on start.
• Tooltip explains that the view-tag reveals a byte of correlation to a passive observer of the RPC.
• Show the active strategy inline on Receive above the scan button.

Acceptance.

• Strategy changes without a reload (worker restarts cleanly)
• Copy reviewed for accuracy against sdk/src/chains/stellar/scanner
• Chosen strategy survives reload
• Unit test covers the three code paths in the scanner dispatch

Files. src/pages/Settings.tsx, src/workers/stellar-scanner.worker.ts, src/components/StellarReceive.tsx, src/i18n/en.json.