Default the auth-required databrowser link to solidos.org/docs/browser/ #362

Summary

The auth-required page in JSS (src/auth/middleware.js:365) hardcodes
https://solidos.solidcommunity.net/?uri=... as the "open in databrowser" link
target. This sends users from any JSS deployment to a single operator's
domain. A better default is https://solidos.org/docs/browser/?uri=...,
which is the SolidOS project's own browser endpoint hosted on GitHub Pages.

Current behavior

// src/auth/middleware.js:365
${is401 ? `<a href="https://solidos.solidcommunity.net/?uri=${encodeURIComponent(baseUrl + request.url)}" ...

Verifiable side-effect: any JSS pod returning 401 generates a databrowser link
pointing at solidos.solidcommunity.net, regardless of operator preference,
deployment domain, or version.

Proposed change

Replace the hardcoded URL with a configurable URL with a sensible default:

• Default: https://solidos.org/docs/browser/?uri=...
• CLI override: --databrowser-url <url> (or equivalent config setting)
• Disable: --databrowser-url="" (empty string suppresses the link entirely)

Why solidos.org/docs/browser/

Verified live: https://solidos.org/docs/browser/ returns HTTP 200 and
honors the ?uri= query parameter for direct pod-resource browsing.

Acceptance

• The 401 / auth-required page links to solidos.org/docs/browser/?uri=<encoded> by default
• --databrowser-url <url> overrides the default at runtime
• --databrowser-url="" (empty) suppresses the link entirely on the auth page
• Existing single-host and reverse-proxy deployments both work
• Tests cover: default behavior, override behavior, disable-via-empty behavior

Notes

• Pure config-change PR; no architectural work required
• solidos.org/docs/browser/ already exists, already serves, already accepts ?uri= — no new infrastructure needed upstream of JSS
• Operators who prefer the legacy solidcommunity.net browser can set the override flag explicitly
• This change does not affect the data island / round-trip-optimization architecture (Round-trip optimization for HTML resource views (#346) #347); JSS continues to ship its own inline databrowser path for unauthenticated read access