Get trader context (Markdown)

Returns a single human- and LLM-readable Markdown briefing for one trader: identity, grade, P&L, position coverage, and freshness. The path accepts an Ethereum wallet address (0x...), a known trader username, or a trd_-prefixed trader ID emitted by this API. Unknown traders still return 200 with a degraded 'not yet synced' document (no 404). The Markdown variant does not emit an ETag and does not support conditional requests; use the JSON variant (drop the .md suffix) for ETag/If-None-Match handling.