Hold every verdict write to a reviewed list of user actions

FR-CULL-13 says evidence never writes a rating, flag, label or trash
membership, and nothing enforced it. tools/traceability/src/verdicts.rs
parses the shipped code with syn and enumerates every write: calls to
the catalog setters and trash recorders, SQL that assigns those columns,
sidecar Amendment::Judgement, and fields named rating/flag/label. Each
site must be in ALLOWED with a reason, as Input (inside a Slint on_*
closure, checked structurally), Relay (its callers are checked in
turn), Carried (a verdict made elsewhere: sidecar and XMP pulls, sync
merge, catalog mirrored to file, duplicates consolidation) or
NotAVerdict. Unlisted sites and stale entries both fail
`cargo test -p traceability`; `traces verdicts` prints the list.

syn and proc-macro2 were already in the lockfile as proc-macro
dependencies; this adds the edges, no new crate and no version change.

Cargo.toml

@@ -134,6 +134,12 @@ serde_json = "1"
 # Slint's Markdown parser, so this adds a dependency edge and no crate; only
 # the HTML writer is needed, not the command-line front end.
 pulldown-cmark = { version = "0.13", default-features = false, features = ["html"] }
+# The verdict-writer check (tools/traceability, FR-CULL-13) reads Rust as Rust:
+# a text scan cannot tell a call from a comment, a test module from shipped
+# code, or which callback closure a call sits in. Both already in the tree as
+# every proc macro's parser; `span-locations` gives a problem its line.
+syn = { version = "2", default-features = false, features = ["full", "parsing", "visit", "printing"] }
+proc-macro2 = { version = "1", default-features = false, features = ["span-locations"] }
 base64 = "0.23"
 
 # Display-server clients, for FR-DSP-8's per-display profile acquisition.