Merge pull request #676: feat(tabs): per-case default session group

Conflict in CLAUDE.md's State Files line resolved by keeping #661's new
config-backup entries and this PR's "case default groups" in state.json.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/wiki/Core-Concepts.md

@@ -13,6 +13,10 @@ Codeman-side configuration:
 
 - Which CLI the Run button should default to.
 - Per-case toggles (Agent Teams, 1M Opus context).
+- A **Default session group** (Case settings…): new sessions of the case land in that tab group of the
+  vertical rail unless you start them from a group's own *New session* or they follow the session that
+  spawned them. *Ungrouped* turns it off. It follows you across devices, never moves existing tabs, and a
+  deleted group simply falls back to Ungrouped.
 - Where it runs, if it is not the local filesystem: see [Location overlays](#location-overlays).
 
 Three ways to get one, all under **New or link a case…** at the bottom of the case picker

docs/wiki/HTTP-API.md

@@ -72,7 +72,7 @@ Roughly 235 handlers across 26 route modules. By domain:
 | ------------------- | -------- | --------------------------------------------------- |
 | System              | 56       | Status, settings, digest, updates, tunnel.           |
 | Sessions            | 34       | Create, input, terminal, wait, last response, kill.  |
-| Cases               | 37       | Create, link, clone, worktrees, remote and docker cases. |
+| Cases               | 39       | Create, link, clone, worktrees, remote and docker cases. |
 | Files               | 17       | Preview, edit, raw, attachments, path picker.        |
 | Orchestrator        | 10       | Plans and phases.                                     |
 | Ralph               | 9        | Loop control and configuration.                       |