fix(mem0-plugin): remove userConfig from plugin.json, add auto-deps install

- Remove userConfig from .claude-plugin/plugin.json — OAuth flow handles
  auth via mcp.mem0.ai, userConfig prompt was redundant and confusing
- Add ensure_deps.sh to install mem0ai SDK into persistent plugin venv
- Add requirements.txt (mem0ai) for dependency tracking
- Wire SessionStart hook to auto-install deps on first run
- Update setup_coding_categories.py to find venv site-packages
- Update onboarding SKILL.md with venv-aware install steps

mem0-plugin/scripts/ensure_deps.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+# Install mem0ai SDK into a persistent venv inside CLAUDE_PLUGIN_DATA.
+# Runs on SessionStart; skips if requirements.txt hasn't changed.
+set -euo pipefail
+
+PLUGIN_ROOT="${CLAUDE_PLUGIN_ROOT:-$(cd "$(dirname "$0")/.." && pwd)}"
+DATA_DIR="${CLAUDE_PLUGIN_DATA:-${HOME}/.mem0/plugin-data}"
+VENV_DIR="${DATA_DIR}/venv"
+REQ_SRC="${PLUGIN_ROOT}/requirements.txt"
+REQ_STAMP="${DATA_DIR}/requirements.txt"
+
+mkdir -p "${DATA_DIR}"
+
+needs_install=false
+
+if [ ! -f "${VENV_DIR}/bin/python3" ]; then
+  needs_install=true
+elif ! diff -q "${REQ_SRC}" "${REQ_STAMP}" >/dev/null 2>&1; then
+  needs_install=true
+fi
+
+if [ "${needs_install}" = "true" ]; then
+  python3 -m venv "${VENV_DIR}" 2>/dev/null || python -m venv "${VENV_DIR}"
+  "${VENV_DIR}/bin/pip" install --quiet --upgrade pip >/dev/null 2>&1 || true
+  if "${VENV_DIR}/bin/pip" install --quiet -r "${REQ_SRC}" 2>/dev/null; then
+    cp "${REQ_SRC}" "${REQ_STAMP}"
+  else
+    rm -f "${REQ_STAMP}"
+    echo "mem0 plugin: failed to install Python dependencies" >&2
+    exit 0
+  fi
+fi