Build lane chrome — title bar, badge, inline rename

The lane title bar becomes real: leading SF Symbol (hand-written names
render leniently, unknown ones fall back to the level default), title
or secondary untitled placeholder, a quiet count badge that counts
exactly the cards the body renders (so the m5 search filter is
followed by construction), and a new-card button. The whole bar is
the reorder drag surface — no grip — with click-vs-movement splitting
select from drag; a pure proposal function maps the drag to an
insertion index and release commits through the Writer's same-parent
degenerate reorder, compacting and retrying when midpoint precision
runs out. Clicking never edits: inline rename is Return on the sole
selected card or Board > Rename for either kind, a third transient
editor beside the placeholder that tracks its target by UUID, commits
on focus loss, discards silently when the target vanishes, and
removes the title key on an empty commit. The new-card placeholder
renders at last — the settled Cmd-N target rule (pure, tested) files
it after the anchor card, at a selected lane's bottom, or into the
last-active lane; Return commits and re-selects the lane, Cmd-Return
also opens the card window, and a failed create discards the overlay.
New Card / New Lane / Rename land in the menus with focused-editor
and read-only validation; rename gets its own WriteOperation case in
the banner vocabulary. 59 new tests.

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

Kanban/Storage/BoardWriter.swift

@@ -1193,6 +1193,14 @@ public enum WriteOperation: Sendable, Equatable, CustomStringConvertible {
     case purge(title: String?)
     case style(title: String?)      // updateIndex on behalf of styling flows (03-board-ui.md)
     case resize(title: String?)     // a lane's `width` — the edge drag and the stepper alike (03-board-ui.md § Lane)
+    /// An inline title editor's commit — the third inline editor's write (04-interactions.md ▸
+    /// Grammar). Its own case rather than a fold into `.style`: "the vocabulary grows with the
+    /// surfaces" is settled (02-architecture.md § Write-failure surfacing, which names
+    /// "Couldn't rename 'Fix login'…" verbatim), and a rename that failed must not tell the user
+    /// the app could not *restyle* something. `title` is the item's title as it stood **before**
+    /// the edit — `updateIndex` enriches it off the document it just read — which is the name the
+    /// user is still looking at when the banner appears.
+    case rename(title: String?)
     case importAttachment(filename: String)
     case listAttachments
     case renumberChildren           // order-maintenance sweep (compaction)
@@ -1218,6 +1226,7 @@ public enum WriteOperation: Sendable, Equatable, CustomStringConvertible {
         case .purge: .purge(title: title)
         case .style: .style(title: title)
         case .resize: .resize(title: title)
+        case .rename: .rename(title: title)
         }
     }
 
@@ -1240,6 +1249,7 @@ public enum WriteOperation: Sendable, Equatable, CustomStringConvertible {
         case let .purge(title): Self.phrase("purge", title)
         case let .style(title): Self.phrase("style", title)
         case let .resize(title): Self.phrase("resize", title)
+        case let .rename(title): Self.phrase("rename", title)
         case let .importAttachment(filename): "import attachment '\(filename)'"
         case .listAttachments: "list attachments"
         case .renumberChildren: "renumber children"