feat: first-boot compose discovery and adopt-first sidebar (#1600)

* feat: add compose discovery for setup preflight and sidebar empty state

Expose read-only compose discovery via GET /api/stacks/discovery and setup

diagnostics. Replace the blank sidebar with path-aware discovery and move

adopt into a dedicated dialog with a three-tab Create Stack flow.

* test: assert post-setup handoff via sessionStorage read-back

The Setup preflight test spied on Storage.prototype.setItem to check the
post-setup adopt handoff. When the jsdom storage probe fails and the test
harness swaps in its in-memory storage stub (which does not extend Storage),
that stub's setItem never touches Storage.prototype, so the spy records zero
calls and the assertion fails even though the component wrote the value.

Read the value back with sessionStorage.getItem instead, matching how every
other storage test in the suite asserts. This is robust to both the native
jsdom storage and the in-memory fallback.

* fix(setup): surface compose discovery as a preflight check row

Drop the Setup discovery banner and non-working Review button. Show

counts as a pass row in EnvironmentChecks (Setup only) and keep

Enter Sencho as the handoff that opens adopt when candidates exist.

* test(setup): cover zero-count discovery row omission

* fix(stacks): widen adopt scan to any yaml and rename into place

Homelab layouts often use nginx.yml or plex.yml. Surface those for
adopt (except overrides), rename to compose.yaml on move so stacks
register, and reset the confirm UI when a move fails.

docs/getting-started/quickstart.mdx

@@ -109,9 +109,9 @@ Below the stack table, **Configuration Status** summarizes notifications, alerts
 
 On the local node, the top navigation includes **Home**, **Fleet**, **Resources**, **Security**, **App Store**, and **Logs**. Depending on license, role, and node context, it can also include **Update**, **Schedules**, **Console**, and **Audit**; hub-only views are hidden when a remote node is active. The right side of the top bar holds global search, notifications, and the profile menu entries **Settings**, **Documentation**, **Feedback**, **Appearance**, and **Log Out**.
 
-The left sidebar is the stack workspace. Below the Sencho brand, it starts with the node switcher, then **Create Stack**, a bulk-mode toggle, and **Scan stacks folder** for importing Compose projects added outside Sencho. Use **Search stacks...** with the **All**, **Up**, **Down**, and **Updates** chips to narrow the list. On a fresh install the stack list is empty until you create a stack or scan a populated `COMPOSE_DIR`.
+The left sidebar is the stack workspace. Below the Sencho brand, it starts with the node switcher, then **Create Stack**, a bulk-mode toggle, and **Scan stacks folder** for re-indexing compose projects added outside Sencho. Use **Search stacks...** with the **All**, **Up**, **Down**, and **Updates** chips to narrow the list. On a fresh install with an empty stack list, Sencho scans your mounted compose directory automatically and shows what it found, including compose files that still need to be adopted into their own subfolder.
 
-Click **Create Stack** in the sidebar and choose **Empty**, **From Git**, or **From Docker Run**. Open **App Store** for a template-driven deploy flow. Once a stack exists, select it in the sidebar or in **Stack health** to open the stack workspace with container health, logs, files, compose editing, and stack actions.
+Click **Create Stack** in the sidebar and choose **Empty**, **From Git**, or **From Docker Run**. Use **Adopt existing files** when Sencho finds compose files that are loose at the compose directory root or one folder too deep (any `.yml` / `.yaml`, not only `compose.yaml`). Loose root files are also auto-promoted into stack folders on the next Sencho restart; adopt is the guided path especially for nested placements. Open **App Store** for a template-driven deploy flow. Once a stack exists, select it in the sidebar or in **Stack health** to open the stack workspace with container health, logs, files, compose editing, and stack actions.
 
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