fix(functions): stop leaking scratch files to trash via bare rm

Verified an agy audit of every bare rm call (the trash-routing C1
shadow) by hand rather than trusting its report. Confirmed correct:
scrub.fish's custom_rm strategy and logs.fish's Ctrl-D delete both
deliberately want trash for a real, user-facing deletion.

Confirmed and fixed three cases where a function's own throwaway
scratch file was going to the user's trash instead of being wiped:
fc.fish's edited-command tmpfile, dng2avif.fish's intermediate PNM
(inconsistent with its own failure-path cleanup two lines up, which
already used -f), and _scrollback_prune_junk.fish's junk log files
(its sibling _prune_terminal_logs.fish already documents this exact
pitfall in its header).

Also went further than the report and classified every bypasses-shadow(rm)
caller found by grep that had never been audited at all:
config-settings.fish and edit.fish (own scratch cleanup, no destructive
data at stake) and key-crypt.fish (--remove deletes the user's real
input file after encryption, genuinely destructive, already documented
in its own header as 'not a secure wipe'). Corrected scrub.fish's tag,
which was missing uses-shadow(rm) for its deliberate trash-routing
branch alongside the bypass branch it already had tagged.

Added a note to the schema doc: rm's flag-based fallback lives inside
the shadow itself, so a bare rm -f/rm -rf call is not the caller
bypassing anything -- only an explicit command rm/builtin rm earns
the tag. This is why dng2avif.fish's fix needed no CLASSIFICATION
change: it already used rm -f, which was never actually the bug --
the missing -f on line 122 was.

functions/_scrollback_prune_junk.fish

@@ -2,7 +2,7 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
 # CLASSIFICATION
-#   bypasses-shadow(cat)
+#   bypasses-shadow(cat,rm), destructive
 #
 # SYNOPSIS
 #   _scrollback_prune_junk [dir]
@@ -29,7 +29,7 @@ function _scrollback_prune_junk --description 'Remove empty, trivial, and Kitty
     # Remove any completely empty log file regardless of source
     for f in $dir/*.log $dir/*.txt
         test -f $f || continue
-        not test -s $f; and rm $f
+        not test -s $f; and command rm -f $f
     end
 
     # Remove any log with only a single meaningful line (e.g. [exited], a lone prompt, or a trivial error)
@@ -37,7 +37,7 @@ function _scrollback_prune_junk --description 'Remove empty, trivial, and Kitty
         test -f $f || continue
         set -l line_count (command cat $f | sed 's/\x1b\[[0-9;:]*[a-zA-Z]//g' | grep -cv '^\s*$')
         if test $line_count -le 1
-            rm $f
+            command rm -f $f
         end
     end
 
@@ -45,7 +45,7 @@ function _scrollback_prune_junk --description 'Remove empty, trivial, and Kitty
     for f in $dir/scrollback_*.log $dir/scrollback_*.txt
         test -f $f || continue
         if command cat $f | sed 's/\x1b\[[0-9;:]*[a-zA-Z]//g' | grep -q 'Enter the new title for this tab below'
-            rm $f
+            command rm -f $f
         end
     end
 end