docs: correct self-host time claim (~90s → ~4 min, honest caveat)

[nbkdoesntknowcoding]

The README quickstart heading claimed self-host takes ~90 seconds, which is wrong. Measured reality (cold-start benchmark, pristine Run 3): clone → live MCP endpoint is ~4 minutes — a one-time image build — and a stone-cold first-ever build can spike toward ~9-10 min because it's I/O-bound on Docker's filesystem, not downloads (native Linux is as fast or faster).

Changes (docs/copy only)

• README.md — heading Quickstart (self-host, ~90 seconds) → Quickstart (self-host in a few minutes), plus an honest intro: "Clone to a live MCP endpoint in about 4 minutes — a one-time image build. (A stone-cold first-ever build can take longer; it's I/O-bound on Docker's filesystem, not downloads. Native Linux is as fast or faster.)"
• scripts/self-host-init.sh — aligned the printed build estimate ("several minutes" → "about 4 minutes", with the stone-cold caveat). The existing "looks idle but isn't / docker compose logs -f" notice is retained.

Scope

• Grepped the whole repo for duration/speed claims. The only wrong self-host claim was the README heading.
• Left out of scope (confirmed): the in-app "Connect in 30 seconds" labels on the client-connection pages — that's a different, accurate claim about connecting an AI client, not the self-host build.
• No Dockerfile, compose, or code-logic changes.