[NF-49] [FRONTEND] Multi-Wallet Portfolio View

Overview

The existing /portfolio page only ever shows the single currently-connected wallet's positions. This issue adds the ability to add and view additional (read-only, not necessarily connected) wallet addresses alongside it, for users managing capital across multiple addresses.

Problem

Users who split capital across multiple wallets (e.g. a hardware wallet for large locked positions and a hot wallet for Flex) currently have to disconnect and reconnect a different wallet, and re-navigate to /portfolio, to check each one — there's no consolidated view.

Proposed Solution

• Add a "Watch another address" action on /portfolio: accepts a Stellar address and adds it (read-only, no signing capability) to a locally-stored watch list (localStorage, keyed by the primary connected wallet, no backend).
• Portfolio page aggregates and clearly labels positions by source address (connected vs. watched), reusing NF-24's SDK batchPositions for efficient multi-address reads.
• Watched addresses can view but not perform actions (Withdraw/Early Exit/Migrate buttons disabled) since the user hasn't proven wallet control over them — only the actually-connected wallet's positions get action buttons.
• Aggregate summary totals (from the existing portfolio summary card) can optionally include or exclude watched addresses via a toggle, clearly labeled.

Acceptance Criteria

• Watched addresses persist across sessions for the connected wallet that added them
• Positions from watched addresses are clearly visually distinguished from the connected wallet's own positions
• No write actions (withdraw/early exit/migrate) are available for watched (non-connected) addresses
• Aggregate summary totals correctly reflect the include/exclude-watched toggle state
• Uses batched position reads (NF-24) rather than one request per watched address

Start at the /portfolio page and inspect the NF-24 SDK batchPositions usage, the existing portfolio summary card, and the localStorage conventions. Trace how connected-wallet positions and actions are rendered, then implement the watch list, address labels, read-only controls, and include/exclude totals so each acceptance criterion is verifiable.