feat(shell): add CachyOS-derived tricks.fish and copy utilities

Adds conf.d/tricks.fish (PATH additions for ~/.local/bin and depot_tools,
bang-bang key bindings, history timestamp override, backup utility) and
functions/copy.fish (smarter cp wrapper that strips trailing slashes from
source directories, fixing a CachyOS-specific cp quirk).

Updates config.fish to explicitly source copy.fish on startup and refactors
several conditional blocks to single-line style for consistency. Syncs
README.md to document all new utilities.

functions/copy.fish

@@ -0,0 +1,14 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+function copy
+    set count (count $argv)
+    if test "$count" = 2; and test -d "$argv[1]"
+        # 'string trim' is built straight into Fish and works everywhere
+        set from (string trim --right --chars=/ $argv[1])
+        set to (echo $argv[2])
+        command cp -r $from $to
+    else
+        command cp $argv
+    end
+end