docker-mailbox v0.3.0 — reader mode

`?reader=true` on message fetch (HTTP + MCP) adds a `body_reader` field —
the HTML body flattened to clean markdown via html2text. Drops styles,
scripts, tracking pixels, and table chrome; keeps headings, inline links,
bold/italic. Built for LLMs that don't want to parse raw HTML.

Original body_text/body_html still returned; reader is additive. Off by
default to keep payload size sane on bulk reads.