Drop the parameter the offline sidecar writer never used

`write_one_sidecar` took an `Option<&NextcloudBackend>` it ignored. It was a
leftover from the shape the write path had before online and offline separated
into two functions: the offline one records to the cache and queues, and has no
server to talk to by definition. A parameter that is always `None` and always
unused says the opposite — that there is a case where it is `Some` — and the
next reader has to check.

The closure it was threaded through is renamed to say what it does rather than
how it is called. `run(None)` needed the reader to know what `None` meant;
`queue_all()` is the sentence.

Also regenerates the traceability matrix, which now records FR-CAT-9's queue.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ui/dr-ui/src/library.rs

@@ -404,10 +404,12 @@ pub fn spawn_sidecar_writes(
             }
         };
 
-        let run = |backend: Option<&NextcloudBackend>| {
+        // Every write, recorded locally and queued. The offline path, and the
+        // fallback whenever a backend could not be built.
+        let queue_all = || {
             let mut report = SidecarReport::default();
             for w in &writes {
-                match write_one_sidecar(backend, &cache, w) {
+                match write_one_sidecar(&cache, w) {
                     Ok(Outcome::Uploaded) => report.written += 1,
                     Ok(Outcome::Queued) => report.queued += 1,
                     Err(e) => {
@@ -421,7 +423,7 @@ pub fn spawn_sidecar_writes(
         };
 
         let report = match rt {
-            None => run(None),
+            None => queue_all(),
             Some(rt) => rt.block_on(async {
                 match NextcloudBackend::new(&creds, &user_id) {
                     Ok(b) => {
@@ -443,7 +445,7 @@ pub fn spawn_sidecar_writes(
                     // will go up with the next drain.
                     Err(e) => {
                         log::debug!("no backend for sidecar upload ({e}); queueing");
-                        run(None)
+                        queue_all()
                     }
                 }
             }),
@@ -553,11 +555,7 @@ fn amend(base: dr_pipeline::Sidecar, w: &SidecarWrite) -> dr_pipeline::Sidecar {
 /// copy when the connection returns — that reconciliation is a *merge*
 /// (FR-NC-9), not an overwrite, so building on a possibly-stale base here does
 /// not cost another device's work.
-fn write_one_sidecar(
-    _backend: Option<&NextcloudBackend>,
-    cache: &SidecarCache,
-    w: &SidecarWrite,
-) -> Result<Outcome, String> {
+fn write_one_sidecar(cache: &SidecarCache, w: &SidecarWrite) -> Result<Outcome, String> {
     let path = sidecar_path(&w.image_path);
     let base = cache.load(&path).unwrap_or_default();
     cache.store(&path, &amend(base, w), true)?;