SafeDrop v1.6.1

Patch — make the desktop install path actually one line. No
protocol changes, no new dependencies.

Added

• scripts/install.sh — one-key installer for macOS + Linux.
  Verifies Python 3.10+, asserts tkinter is importable (with a clear,
  platform-specific fix on failure), creates a hermetic venv at
  ~/.local/share/safedrop/venv, installs safedrop[mcp] from PyPI
  (or --from-release against the latest GitHub Release wheel), and
  drops safedrop-gui / safedrop / safedrop-mcp /
  safedrop-mcp-tokens / safedrop-agent / safedrop-beacon
  launchers into ~/.local/bin. Idempotent.
• scripts/install.ps1 — PowerShell counterpart for Windows. Venv
  lives at %LOCALAPPDATA%\SafeDrop\venv; .cmd launchers under
  %LOCALAPPDATA%\SafeDrop\bin. Same flow, same error messages.

Changed

• README "Quick start" now leads with the one-line install:

  curl -fsSL https://raw.githubusercontent.com/gclinian/SafeDrop/main/scripts/install.sh | bash
  

  (and the iwr | iex Windows equivalent). The previous
  git clone + venv + pip install -e flow is preserved under a new
  Desktop — manual install subsection for the security-conscious.
• docs/landing.html install snippet updated to match.

Tests

• Smoke-verified scripts/install.sh --from-release against the
  published v1.6.0 wheel: pulls the .whl from GitHub Releases,
  installs into a fresh venv, launchers fire correctly,
  safedrop ls runs without errors.