fix(cli): parse get-memory response correctly

[nicoloboschi]

Problem

hindsight memory get <bank> <id> fails with a misleading "Invalid API response format" error whenever the memory has any entities.

The CLI deserializes the response into a hand-written local MemoryUnitDetail struct that had drifted out of sync with what GET /memories/{memory_id} (MemoryEngine.get_memory_unit) actually returns:

• entities — the API returns a flat list of canonical-name strings (["Alice", "Bob"]), but the struct expected a list of {id, name} objects. serde_json::from_value errors on the type mismatch, and the friendly error layer renders it as "Invalid API response format".
• fact type — the API field is type, but the struct renamed it to fact_type, so even when parsing succeeded the Type: line always printed UNKNOWN.

The endpoint returns an untyped JSON body in the OpenAPI spec, so the generated client never validates it — the mismatch only blows up in the CLI handler. These commands had no test coverage (the docs only demonstrate them with curl), so the drift went unnoticed.

Fix

• entities: Option<Vec<String>> (was Vec<EntityRef>); removed the now-unused EntityRef struct.
• Rename the type field serde alias from fact_type → type.
• Update the entity display loop to print the canonical-name strings.
• Add a comment on the struct noting it must mirror get_memory_unit.

Tests

Added two regression tests deserializing realistic API payloads (full + minimal). Both fail before the fix, pass after. cargo test green; ./scripts/hooks/lint.sh clean.

Notes

hindsight memory history was mentioned alongside this in a bug report but is not affected — it pretty-prints the raw JSON value with no struct parsing. A missing/non-observation memory there returns 404 ("API request failed (404)"), not a format error.