docs(agents): add a GEMINI.md pointer to the maintained instructions (#87)

Adds a `GEMINI.md` pointer file to this repository.

**Why.** An estate-wide census found a large asymmetry in
agent-instruction
files: `CLAUDE.md` was present almost everywhere, `GEMINI.md` in a
handful of
repositories. Any coding agent that looks for `GEMINI.md` and does not
find one
proceeds with no repository-specific instructions at all.

**This file is a pointer, not a second copy of the instructions.**
Duplicating
guidance across per-agent files guarantees the copies drift. The pointer
redirects to whichever file this repository actually maintains —
`AGENTS.md`
where one exists, otherwise `CLAUDE.md` — and says to retarget it at
`AGENTS.md` when one lands.

**How this commit was built.** The change was made with git plumbing
against
`origin/<default branch>`, not by staging a working tree. The branch
contains
exactly one commit adding exactly one file, and carries none of the
unrelated
local state present in this checkout. A per-repository assertion
required
`git diff --name-only <base> <commit>` to equal the expected path set
exactly,
or the branch was never created.

**This PR is opened as a draft on purpose.** It is part of a bulk
campaign and
is not requesting a merge. Review and merge at your discretion.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_011eQ7hibx92N7fBDtwgReWk

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: hyperpolymath

GEMINI.md

@@ -0,0 +1,4 @@
+# Pointer
+
+The canonical, tool-agnostic instructions for this repository are in
+**[AGENTS.md](./AGENTS.md)**. Read that file. Do not duplicate rules here.