Add curl-pipe installer, uninstaller, and contributor bootstrap

End-user installation collapses to a single command:

  curl -fsSL https://gitea.cahlen.com/nokeo08/Move/raw/branch/master/install.sh | sh

Changes:

- install.sh rewritten as a POSIX sh, curl-pipeable end-user installer.
  Honors XDG_DATA_HOME and XDG_BIN_HOME (de facto). Idempotent via a
  version-marker file at $INSTALL_DIR/.installed-version; MOVE_FORCE=1
  overrides. Hard-fails if Bun is missing (no auto-install). Includes
  a safety guard refusing rm -rf on too-broad install dirs.
- uninstall.sh added; same curl-pipe pattern, shared XDG path
  resolution, leaves Bun alone.
- dev-setup.sh added (= the previous install.sh content, retitled for
  contributors and pointing at bun run start / bun link / install.sh).
- README updated: curl one-liner Install section, XDG behavior tables,
  new Uninstall section, new 'For contributors' section, Files table
  rows for all three scripts.

uninstall.sh

@@ -0,0 +1,56 @@
+#!/usr/bin/env sh
+#
+# uninstall.sh - End-user uninstaller for the `move` CLI.
+#
+# Curl-pipe ready:
+#
+#   curl -fsSL https://gitea.cahlen.com/nokeo08/Move/raw/branch/master/uninstall.sh | sh
+#
+# Removes the `move` wrapper from $XDG_BIN_HOME and the install tree from
+# $XDG_DATA_HOME/move. Does NOT remove Bun — that's your runtime, not ours.
+#
+# Env vars (must match what install.sh used):
+#   XDG_DATA_HOME Source install root (default $HOME/.local/share).
+#   XDG_BIN_HOME  Wrapper install root (default $HOME/.local/bin).
+#
+# POSIX sh; no bashisms.
+
+set -eu
+
+INSTALL_DIR="${XDG_DATA_HOME:-$HOME/.local/share}/move"
+BIN_DIR="${XDG_BIN_HOME:-$HOME/.local/bin}"
+WRAPPER="$BIN_DIR/move"
+
+die() {
+    printf 'Error: %s\n' "$1" >&2
+    exit 1
+}
+
+# Same safety guard as install.sh: refuse to wipe a directory that points
+# somewhere catastrophic.
+case "$INSTALL_DIR" in
+    '' | '/' | "$HOME" | "$HOME/" | '/move')
+        die "refusing to operate on INSTALL_DIR='$INSTALL_DIR' (too broad)"
+        ;;
+esac
+
+REMOVED_SOMETHING=0
+
+if [ -e "$WRAPPER" ] || [ -L "$WRAPPER" ]; then
+    rm -f "$WRAPPER"
+    printf 'Removed %s\n' "$WRAPPER"
+    REMOVED_SOMETHING=1
+fi
+
+if [ -d "$INSTALL_DIR" ]; then
+    rm -rf "$INSTALL_DIR"
+    printf 'Removed %s\n' "$INSTALL_DIR"
+    REMOVED_SOMETHING=1
+fi
+
+if [ "$REMOVED_SOMETHING" = "0" ]; then
+    printf 'Nothing to remove. Checked %s and %s.\n' "$WRAPPER" "$INSTALL_DIR"
+    exit 0
+fi
+
+printf '\nUninstalled. (Bun was not touched.)\n'