fix(activity): show selected watch-only wallet transaction history

[BitHighlander]

Problem and resulting behavior

In watch-only mode, Activity still queried the live wallet scope. With no device connected it returned no rows, and Rescan tried to derive addresses over USB, so the selected saved wallet appeared to have no transaction history.

Activity and asset previews now read the selected snapshot's wallet-scoped rows. Rescan uses its saved public addresses and Bitcoin account xpubs without device derivation. The snapshot is checked again before writes, so a wallet switch or hidden session cannot attach results to another wallet. Bitcoin-only snapshots use a stable scope derived from their saved xpubs because they have no Ethereum seed address. Failed scans show an error instead of “Up to date.” A saved swap can open read-only details in watch-only mode.

Validation

• 32 targeted tests pass, including watch-only scope, Bitcoin-only boundary, and Blockbook history cases.
• Vite build and backend bundle pass from a current develop worktree.
• git diff --check passes.

Limits

• An existing full-firmware snapshot without a stored seed address must be connected once to establish its wallet identity. The UI reports that requirement explicitly.
• A saved chain without a public address or account xpub cannot be rescanned; the UI reports that missing data.
• This PR does not change swap economics or signing paths. It may need a small conflict resolution in src/bun/index.ts if the swap settlement PR merges first.