heph.nvim: run e2e via mise run test-nvim, drop the Makefile

Make mise the dev entrypoint for the headless e2e suite, matching the repo's
mise-tasks convention (auto-discovered, shows in `mise tasks`). Dev relies on
system-installed nvim + rustc; CI will provide them via Dagger (slice 11c).
The self-contained shim runner is unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

mise-tasks/test-nvim

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+#MISE description="Run the heph.nvim headless e2e suite (builds hephd, drives nvim --headless)"
+
+# Dev path: uses system-installed nvim + rustc. CI runs the same suite inside a
+# Dagger container that provides them (tech-spec §9, slice 11c). The runner is
+# self-contained (tests/e2e/runner.lua) — no external nvim plugins, no network.
+
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$ROOT"
+
+if ! command -v nvim >/dev/null 2>&1; then
+  echo "error: nvim not found on PATH (install Neovim >= 0.10)" >&2
+  exit 1
+fi
+
+echo "== building hephd (debug) =="
+cargo build -p hephd
+
+export HEPHD_BIN="$ROOT/target/debug/hephd"
+
+echo "== heph.nvim headless e2e =="
+cd "$ROOT/heph.nvim"
+nvim --headless -u NONE -c "luafile tests/e2e/run.lua"