Widen the selectable agent tooling roster beyond the initial four

#13 ships selection for Claude Code, Cursor, Copilot, Gemini CLI and Codex, with the ownership map built to be extended. Other tools developers actually use — Windsurf, Zed, Aider, JetBrains Junie among them — read their own pointer paths and get nothing today.

Each addition is small (one pointer file at the tool's native path, one entry in the map, one row in the per-tool file-set test), so this is a rolling item to pull from as tools are requested rather than one batch of work. Worth confirming a tool is still actively used before adding it — a stale pointer file is a maintenance cost with no reader.

Came out of an ideation session around #13, not a scoped request.

Start by reading the selection work from #13, then inspect the ownership map and the per-tool file-set test mentioned in the issue. Choose one actively used tool, confirm its native pointer path, and consider the work done when its pointer file, map entry, and test row are all represented.

Written by the indexing model from the issue text.