feat: XDG Base Directory compliance, --uninstall flag, and xclip advisory

- Resolve all paths via $XDG_CONFIG_HOME, $XDG_DATA_HOME, and
  $XDG_RUNTIME_DIR with conventional fallbacks (~/.config,
  ~/.local/share, /tmp); BIN_DIR stays ~/.local/bin (no XDG standard)
- Add --uninstall: removes symlink, desktop entry, and data dir with
  colored per-step output; prompts to remove config when interactive,
  skips silently when not; post-run verification reports any failures
- Warn in --check-deps and --install when only xclip is present —
  xclip operates through XWayland and can be unreliable on Wayland
- Normalize dependency messages to package names (wl-clipboard, xclip)
- Update README: XDG paths in install steps, --uninstall in usage,
  xclip advisory in prerequisites
- Fix test sandbox: export XDG_CONFIG_HOME and XDG_DATA_HOME so the
  overridden HOME is respected; add install (test 15) and uninstall
  (test 16) coverage; add cp and ln to mocked tool set

tests/run_tests.sh

@@ -59,9 +59,13 @@ MOCK
 chmod +x "$BIN_DIR/curl"
 ln -s /usr/bin/mv "$BIN_DIR/mv"
 ln -s /usr/bin/tr "$BIN_DIR/tr"
+ln -s /usr/bin/cp "$BIN_DIR/cp"
+ln -s /usr/bin/ln "$BIN_DIR/ln"
 
 export PATH="$BIN_DIR"
 export HOME="$TEST_DIR"
+export XDG_CONFIG_HOME="$TEST_DIR/.config"
+export XDG_DATA_HOME="$TEST_DIR/.local/share"
 export WAYLAND_DISPLAY=wayland-0
 export XDG_CURRENT_DESKTOP=KDE
 
@@ -232,6 +236,44 @@ else
   echo "  Actual output: $output"
 fi
 
+# 15. Install — files placed in correct XDG directories
+it "installs files to XDG directories"
+# Clear any artifacts from earlier tests before verifying a clean install
+rm -rf "$XDG_DATA_HOME/color-tool" \
+       "$XDG_DATA_HOME/applications/color-tool.desktop" \
+       "$HOME/.local/bin" 2>/dev/null || true
+install_out=$("$COLOR_TOOL" --install 2>&1)
+if [[ -f "$XDG_DATA_HOME/color-tool/color-tool" ]] &&
+   [[ -f "$XDG_DATA_HOME/color-tool/wl-colorpicker-plasma.py" ]] &&
+   [[ -L "$HOME/.local/bin/color-tool" ]] &&
+   [[ -f "$XDG_DATA_HOME/applications/color-tool.desktop" ]] &&
+   [[ -f "$XDG_CONFIG_HOME/color-tool/config.toml" ]]; then
+  echo "PASS"
+  passed=$((passed + 1))
+else
+  echo "FAIL"
+  echo "  Install output: $install_out"
+  echo "  Files found:"
+  /usr/bin/find "$TEST_DIR/.local" "$TEST_DIR/.config" \( -type f -o -type l \) 2>/dev/null | /usr/bin/sort || true
+fi
+
+# 16. Uninstall — removes installed files, config is kept in non-interactive mode
+it "uninstalls installed files (keeps config)"
+uninstall_out=$("$COLOR_TOOL" --uninstall 2>&1)
+if [[ ! -e "$HOME/.local/bin/color-tool" ]] &&
+   [[ ! -L "$HOME/.local/bin/color-tool" ]] &&
+   [[ ! -d "$XDG_DATA_HOME/color-tool" ]] &&
+   [[ ! -f "$XDG_DATA_HOME/applications/color-tool.desktop" ]] &&
+   [[ -f "$XDG_CONFIG_HOME/color-tool/config.toml" ]]; then
+  echo "PASS"
+  passed=$((passed + 1))
+else
+  echo "FAIL"
+  echo "  Uninstall output: $uninstall_out"
+  echo "  Files still present:"
+  /usr/bin/find "$TEST_DIR/.local" "$TEST_DIR/.config" \( -type f -o -type l \) 2>/dev/null | /usr/bin/sort || true
+fi
+
 # ── Cleanup ───────────────────────────────────────────────────────────────────
 echo "---------------------------------------"
 echo "Result: $passed/$total tests passed."