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/scrub.fish

@@ -5,7 +5,7 @@
 #   01-file-and-directory
 #
 # CLASSIFICATION
-#   bypasses-shadow(rm), destructive
+#   uses-shadow(rm), bypasses-shadow(rm), destructive
 #
 # SYNOPSIS
 #   scrub [-a] [-d] [-h]