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.

docs/function-classification-schema.md

@@ -72,3 +72,10 @@ schema's own rollout caught several false positives this way: a piped
 `read` misread as an interactive prompt, a documented `--yes` flag missed
 as an escape hatch, and cleanup of a function's own temp output flagged
 as `destructive` despite the explicit exclusion above.
+
+`rm` specifically has its own internal flag check (any flag other than
+`-r`/`-R`/`--recursive` falls back to `command rm` *inside the shadow
+itself*, before it ever touches trash) — a caller writing plain `rm -f`
+or `rm -rf` is not bypassing anything itself, the shadow is. Only tag
+`bypasses-shadow(rm)` when the caller explicitly writes `command rm` or
+`builtin rm`; a bare `rm -f`/`rm -rf` call gets no shadow tag at all.