fix(tabs): inline rename review fixes

Reopening the editor over a rename still in flight filled it from the name
the server had not replaced yet, so dismissing it (blur commits) queued the
old name behind the new one and undid the rename. The queue now records the
newest queued name per session (_inlineRenamePending, cleared with the queue
entry), and a reopened editor takes its prefix, input and "unchanged"
comparison from it. An untouched confirm sends nothing more.

A failed write only toasted while its editor was still current. The queue
reports the failure itself now, and the editor only puts its label back.

One rejected task blocked every later rename of that session until reload.
Each task now chains from a settled predecessor, the local apply after a
successful PUT is guarded, and the queue entry is cleaned up on either
outcome.

The rail and sidebar editor's 4rem floor moves from a stylesheet
`!important` into the inline min-width startInlineRename already writes per
layout (0 in the header strip, 4rem in the rail and sidebar).

Tests: the reopened-editor case now expects only "First" to be sent; new
cases cover a 500 answered after the editor is gone and a throw in
updateSubagentParentNames; the long-prefix check runs in the sidebar and
detailed sidebar too and asserts the inline floor; the header strip editor
keeps min-width 0.

src/web/public/styles.css

@@ -1867,15 +1867,14 @@ html[data-tab-orientation='vertical'] .tab-rail .session-tab .tab-name-prefix {
   text-overflow: ellipsis;
 }
 
-/* The input always keeps room to type. `!important` beats the editor's inline
-   `min-width: 0`, which the header strip's fixed-width editor relies on. */
+/* The input takes the rest of the row. Its 4rem floor is the editor's own
+   inline min-width (startInlineRename picks it per layout). */
 :is(
   html[data-tab-orientation='vertical'] .tab-rail,
   html[data-session-list='sidebar'] .session-sidebar
 ) .tab-name-renaming .tab-rename-input {
   flex: 1 1 0;
   width: auto;
-  min-width: 4rem !important;
 }
 
 /* A compact rail row has no room for both the editor and its adornments, so