feat(tabs): place new, child and web tabs into groups - #528

- Pointer drag: a press released outside the rail no longer lingers. The
  release is heard on window while a press is pending, a move with the
  primary button up cancels it, a new press cancels any previous drag, and
  an existing Escape listener is removed before another is added, so no
  orphaned capture listener can swallow Escape before the terminal.
- Inline group rename: a commit by blur leaves focus where the user put it;
  Enter and Escape still return focus to the header.
- A failed layout read while edits are pending keeps the held layout and the
  editor and re-reads once the write settles, so a 409 is still rebased.
  Dropping unsaved work now always says so in a toast.
- "Move to <group>" quotes the group name (with a matching zh-CN pattern), so
  a group named "New group" or "ungrouped" no longer reads or translates like
  the fixed entries.
- The group menu glyph stays visible under (hover: none).
- The sessionStorage replay copy carries { owner, baseVersion, savedAt } and is
  ignored for another owner, after 60 s, or against an older layout. A move
  with no anchor carries no index, so a replay keeps the row last.
- A 400 that survives the re-read is reported as "Could not save tab groups."
- closeTabRailActionMenu() no longer removes the group menu's DOM.
- Cancelling "Delete group" returns focus to the header.
- Stale comments updated.

Two problems with renaming a tab in the vertical rail, both easier to hit now
that the grouped rail has its own inline editor beside the session one.

Writes. A committed rename PUT its name and only applied the answer if the
same editor was still open when it came back. Reopening the editor before the
PUT answered (F2 or right-click again, or starting a group rename, which
cancels the session editor) threw the confirmed name away, so the tab kept
showing the old name until an SSE frame happened to repaint it. Two quick
renames also raced as two concurrent PUTs. Inline renames now go through a
per-session queue: one PUT at a time in the order they were made, the
confirmed name applied to app.sessions whatever happened to the editor, and
the "already that name" check made when the write runs rather than when Enter
is pressed, so confirming the name still on screen over a write in flight is
a real write.

Layout. The editor (a flex row) could not shrink below the input's intrinsic
width, so a long w<n>-<case> prefix pushed the label past its row: the prefix
slid out of view in the detailed rows and the input was clipped mid-word in
the compact rail. The label now has min-width 0, the prefix gives way first
(down to 2rem, with an ellipsis), the input keeps 4rem, and in the compact
rail the row's adornments step aside while the name is edited. The detailed
rows' three-line clamp also outranked the shared unclamp rule, which is what
the existing "unclamped editor" browser test caught; it is restated there.

Header strip, sidebar and flat-rail markup are unchanged.

Tests (test/inline-rename.test.ts, browser suite): the unclamp check runs for
simple and detailed rows; a write-ordering describe covers ordering, a
reopened editor cancelled over a confirmed write, a re-sent unchanged name and
a group rename taking over; a long-prefix describe drives real rows from a
live session in simple, detailed and compact rails.

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.

New sessions, spawned child sessions and saved web tabs now land in tab
groups instead of always starting in Ungrouped.

New session in a group:
- The group menu gains "New session" (first item). It expands a collapsed
  group and runs ONE launch with the current case and run mode; a launch
  already in flight is reported, not queued.
- run({ count, tabGroupId }) threads the group through every launch path
  (local POST /api/sessions, remote/docker and external-CLI
  /api/quick-start). The count overrides the steppers for that launch only.
- Server: POST /api/sessions and /api/quick-start accept an optional
  tabGroupId (Zod, 1-100 chars; null/empty is a 400). The routes pass it to
  addSession(), and TabLayoutService.sessionCreated() places the session at
  the end of that group in the SAME versioned write that first records it.
  The session is added to the live map inside the owner lock (with a
  rollback when the write fails), so no queued layout edit can commit it
  first. The group is looked up in the creating owner's own layout, so an
  unknown, deleted or foreign id is ignored instead of failing the spawn. An
  explicit group is a hand placement: a child placed this way is manual.
- The create response carries the committed tabLayout (only when tabGroupId
  was sent), adopted before the new tab is drawn. Responses without the
  field are unchanged.

Child sessions (parentSessionId / X-Codeman-Parent-Session):
- A child nobody placed follows its parent: the server's existing
  normalization already puts it after the parent's rows; the browser now
  draws a not-yet-stored child there too (project({ parents })) and, while
  groups exist, adopts the server's order instead of echoing its own append
  back through PUT /api/session-order (which pinned every child manual).
- The row menu says where a child sits (follows, placed by hand, parent
  closed, parent loop) and offers "Follow parent again" only to a hand-placed
  child. A child whose parent is gone stands on its own and is never
  re-adopted.

Saved web tabs:
- Web tabs are layout refs like sessions; openness stays per device. A
  grouped web tab shows (and takes an Alt+N slot) only while open here and
  reopens where the layout keeps it. Pinned by tests; no behaviour change.

Unchanged: the flat rail and header strip (markup, HTML5 drag, append and
save on create), the tree semantics and single tab stop, sessionOrder and
Alt+N, and every request that does not send tabGroupId.