Problem

Since the #433/#435 landing-page work, startup seeds /index.html, /.acl, and /index.html.acl into DATA_ROOT (skip-if-exists). This also happens in --public mode, where:

• WAC is bypassed, so the seeded ACLs are never consulted — they are dead files.
• The page's only dynamic behaviour — the HEAD-adaptive Sign up / Sign in buttons (Refine seeded landing page: mode-agnostic copy + HEAD-adaptive Sign up/Sign in (#427) #435) — is meaningless without auth.

For the serve-a-directory use case that --public was created for (#107 explicitly lists the jsserve wrapper as a primary motivation: "use JSS as a simple 'just serve this folder' tool like npx serve"), this writes three files into the user's project directory.

Reproduced with jss start --root <dir> --public on 0.0.210: the served tree gains index.html, .acl, index.html.acl. This regressed servejss's "like serve" behaviour — early JSS versions left the served directory untouched.

Fix

Skip seedServerRoot when options.public is set, alongside the existing read-only skip (src/server.js). Operators who want a landing page in public mode can still create /index.html by hand — skip-if-exists already honours it. Regression tests in test/server-root.test.js (public mode seeds nothing; container listing + file reads still work).

The two features were built for disjoint audiences — the landing page for pod providers (#276 / #303: "new pod providers had to build a landing page from scratch"), --public for serve-style file serving (#107) — and no point in the #276→#435 design history considered the --public case, so the collision is an oversight rather than a decision.

Considered alternatives

• Explicit --no-root-page flag — leaves bare jss --public polluted by default (the exact complaint) and adds plumbing; explicitness only helps when the default is right.
• servejss deletes seeded files post-start — racy, churns file watchers, risks deleting a legitimate user-owned index.html unless it fingerprints the template.
• Virtual (never-written) landing page — the deeper Default index.html for server root #276 redesign; orthogonal and can layer on later, at which point the public-mode skip becomes redundant rather than wrong.

Refs #107, #276, #433, #435, #459, #108.