desktop: render and open nostr:naddr long-form references

## Summary

The Desktop client does not currently render `nostr:naddr1...` references as an openable entry point. Markdown handling only preserves the custom `buzz://message` scheme, so both bare NIP-21 `nostr:naddr` references and explicit Markdown links are inert or stripped.

## Proposed scope

Add Desktop support for opening NIP-23 long-form references (`kind:30023`) inside Buzz:

- recognize bare `nostr:naddr1...` text and explicit Markdown links;
- decode and validate the NIP-19 address with the existing `nostr-tools` dependency;
- render a dedicated interactive link/pill;
- query the current workspace relay using the exact coordinate (`kind`, author pubkey, and `d` identifier);
- open an in-app dialog with loading, success, not-found, error, and retry states;
- leave malformed references, secret-key URIs, unsupported addressable kinds, and references inside code spans/fences non-interactive.

## Security and community boundary

The first version should ignore relay hints embedded in the `naddr` and only query the active workspace relay. This preserves the current community boundary and avoids sending authenticated requests to attacker-controlled relay URLs.

## Out of scope

- A generic viewer for every addressable event kind.
- New relay APIs, event kinds, migrations, or dependencies.
- Mobile support in the same PR; mobile parity can follow as a focused change.

## Acceptance criteria

- Bare and explicit Markdown `nostr:naddr` references for `kind:30023` are openable in Desktop.
- Clicking opens an in-app long-form viewer and does not depend on an OS-level `nostr:` handler.
- The relay query includes `kinds:[30023]`, `authors:[pubkey]`, and `#d:[identifier]`.
- Relay hints are ignored in v1.
- Invalid/unsupported/private-key/code-block text is not made interactive.
- Existing HTTP(S), `buzz://message`, mention, and channel-link behavior remains unchanged.
- Unit, Tauri, and Desktop E2E coverage is included, along with the required UI screenshot evidence.

Start by locating the Desktop Markdown handling that currently preserves buzz://message, then trace the existing relay-query and in-app dialog paths. Use the Unit, Tauri, and Desktop E2E coverage entry points named in the issue, and verify that valid kind:30023 references open while invalid, unsupported, private-key, relay-hinted, and code-block cases remain non-interactive.

Written by the indexing model from the issue text.