feat: nav header on data-browser pages

[melvincarvalho]

Summary

The data-browser previously dropped the user on a wall of rendered JSON-LD with no navigation chrome. Now every resource our browser renders gets a small nav strip above the data:

```
[↑ Up] [Home] [Account] [Docs]
─────────────────────────────────
{ ... rendered JSON-LD ... }
```

• Up navigates one path segment higher (e.g. `/public/links.jsonld` → `/public/`; `/profile/` → `/`). Hidden at the pod root.
• Home, Account, Docs link to the corresponding jspod-owned pages.
• Visually consistent with the cream + card style of welcome.html / account.html / signin.html.

Implementation

`data-browser.js` grows by ~540 bytes (988 → 1528). New module:

```js
const p = window.location.pathname;
const up = (p === '/' || !p)
? null
: (s => { const i = s.lastIndexOf('/'); return i === 0 ? '/' : s.slice(0,i) + '/'; })(p.replace(//$/, ''));
const nav = '

' + (up ? `↑ Up` : '') + 'HomeAccountDocs';
```

CSS for `.jspod-nav` is in the same injected style block (same overall card + cream visual language as the rest of jspod's pages).

Test plan

• `node --check data-browser.js` — syntax OK
• Up calculation correct for: `/`, `/profile/`, `/public/`, `/public/links.jsonld`
• After merge + publish 0.0.25: visit `/profile/` — nav strip should appear above the JSON-LD with all four links; Up should go to `/`

Bumps jspod to 0.0.25.

Refs #1