docs(ui): update the versioning-capability comments for the new backend split

The SourceTable and Restore doc comments still named S3 and the local folder
as the destinations that cannot keep versions, which is now false: both keep
real versions in a `.driven-versions` area, and SFTP is the only exception.
Comment-only; the components already read the capability from the descriptors
rather than a hardcoded list.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019xKUm9vH4ifb5LHR5szy1v

Author: pmaxhogan

ui/src/components/SourceTable.vue

@@ -122,11 +122,12 @@ const accountEmailById = computed<Record<string, string>>(() => {
  *
  * This genuinely differs per backend rather than being a wording choice, so a
  * single sentence could only ever be wrong somewhere: Drive keeps a superseded
- * object in its trash (recoverable for ~30 days), while an S3 or local-folder
- * destination has no trash and the re-upload lands on the SAME deterministic key,
- * overwriting the previous copy. The versioning panel used to state Drive's
- * behaviour unconditionally, directly contradicting the S3 setup screen's own
- * "S3 has no trash" warning inside the same app.
+ * object in its trash (recoverable for ~30 days), an S3 or local-folder
+ * destination keeps it in a `.driven-versions` area Driven owns there (pruned to
+ * the per-source limit, and NOT a recovery path for deletions), and SFTP keeps
+ * nothing at all. The versioning panel used to state Drive's behaviour
+ * unconditionally, directly contradicting the S3 setup screen's own "S3 has no
+ * trash" warning inside the same app.
  *
  * Unseeded / unknown backends fall back to the neutral `default`, because
  * `BackendKind::ALL` is Rust-owned and gains entries ahead of the locale file.
@@ -141,8 +142,9 @@ function retentionNote(accountId: string): string {
  * Issue #220: the destination CAPABILITY descriptors, joined to a source by its
  * account's `backendKind`. Fetched rather than hardcoded, following #219: the set
  * of backends and what each can do is Rust-owned (`driven_backend::descriptors()`),
- * so a UI-side "S3 and local cannot version" list would silently rot the moment a
- * backend's create path changes.
+ * so a UI-side list of which backends can version would silently rot the moment
+ * one gains or loses the ability - as S3 and the local folder did when #220 part 2
+ * gave them a real version store.
  */
 const backends = ref<BackendDto[]>([]);
 async function loadBackends(): Promise<void> {
@@ -159,10 +161,12 @@ async function loadBackends(): Promise<void> {
 /**
  * Whether this source's DESTINATION can really keep previous versions.
  *
- * A destination whose create key is derived from the file name (S3, local folder)
- * re-uploads over the previous copy, so a retained version points at the CURRENT
- * bytes and "restore as of an earlier date" would return today's content while
- * reporting success (issue #220). The editor is not offered there.
+ * A destination that cannot put the superseded bytes under an object of their own
+ * re-uploads over the previous copy, so a retained version would point at the
+ * CURRENT bytes and "restore as of an earlier date" would return today's content
+ * while reporting success (issue #220). Since part 2 that is SFTP alone - Drive,
+ * S3 and the local folder all keep the old bytes - but the answer is read from the
+ * descriptors, never assumed. The editor is not offered where it is false.
  *
  * An UNKNOWN or not-yet-loaded backend resolves PERMISSIVE, matching the house
  * rule from #219 (`setup.ts` / `AddSourceWizard.vue` both `?? true`) so a

ui/src/views/Restore.vue

@@ -97,11 +97,13 @@ const retentionNote = computed<string>(() => {
  * Issue #220: whether the BROWSED source's destination can really serve an older
  * version, so the point-in-time picker is honest to offer.
  *
- * Where the destination's create key is derived from the file name (S3, local
- * folder) a changed file's re-upload overwrote the previous bytes, so a restore
- * "as of" an earlier date would return the CURRENT content while reporting that it
- * restored an older version. The backend refuses such a restore fail-closed; this
- * stops the app OFFERING it in the first place.
+ * Where the destination cannot put the superseded bytes under an object of their
+ * own, a changed file's re-upload overwrote them, so a restore "as of" an earlier
+ * date would return the CURRENT content while reporting that it restored an older
+ * version. Since #220 part 2 that is SFTP alone - Drive, S3 and the local folder
+ * all keep the old bytes - but the answer is read from the descriptors, never
+ * assumed. The backend refuses such a restore fail-closed; this stops the app
+ * OFFERING it in the first place.
  *
  * Unknown / not-yet-loaded resolves permissive (the #219 house rule) - the control
  * must not blink away on every mount, and the backend is the real gate.
@@ -429,9 +431,9 @@ async function onClearSearch(): Promise<void> {
            each file as it was backed up at that instant.
 
            Issue #220: only offered where the destination can really keep previous
-           versions. On a destination whose create key is derived from the file
-           name the older bytes were overwritten, so this control could only ever
-           hand back the current content while claiming otherwise. -->
+           versions. Where the superseded bytes were overwritten rather than
+           archived aside, this control could only ever hand back the current
+           content while claiming otherwise. -->
       <label v-if="canRestoreAsOf" class="flex items-center gap-1.5 text-sm">
         <span class="text-zinc-600 dark:text-zinc-400">{{ t("restore.asOf.label") }}</span>
         <input