docs: Update README "Help wanted": remove #91

Author: lxsaah

.gitattributes

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README.md

@@ -207,7 +207,6 @@ See the [MCP server docs](tools/aimdb-mcp/) for Claude Desktop and other editors
 
 We're a small team building something ambitious. The fastest way to help is to take on a scoped piece of it. Each of these is sized for a few hours and includes file pointers, acceptance criteria, and a place to ask questions:
 
-- [#91 — `is_*_error()` predicates for `DbError`](https://github.com/aimdb-dev/aimdb/issues/91) · 1–2h · core
 - [#92 — `no_std` `Display` for `DbError` should include numeric fields](https://github.com/aimdb-dev/aimdb/issues/92) · 2–3h · core · embedded
 - [#93 — Minimal example: `hello-single-latest`](https://github.com/aimdb-dev/aimdb/issues/93) · 2–3h · docs
 - [#95 — CLI: add `aimdb instance ping` subcommand](https://github.com/aimdb-dev/aimdb/issues/95) · 3–4h · cli