docs: lean-build behavior + nav placement + fix stale prod plugin list

- PLUGINS.md: new 'Lean per-site builds' section (backend/frontend/DB layers,
  manifest-less core frontends always ship, menus gated to staged routes).
- PLUGIN-HOOKS.md: get_navigation_items sidebar placement (position ranges ->
  Assets/Information sections, section override, icon key).
- DEPLOY-WINDOWS-IIS.md: fix stale plugin list (equipment -> machines, complete
  the bundled set), add apply-profile + prune-schema flow.

docs/PLUGIN-HOOKS.md

@@ -174,7 +174,9 @@ isolated in prod, re-raised in dev/test).
 
 ### `get_navigation_items() -> List[Dict]`
 
-Returns navigation menu items.
+Returns navigation menu items. A plugin owns its own sidebar entry here, so it
+appears when the plugin is installed and disappears when it is not (including in
+a lean per-site build that omits the plugin).
 
 ```python
 class ComputersPlugin(BasePlugin):
@@ -187,6 +189,26 @@ class ComputersPlugin(BasePlugin):
         }]
 ```
 
+**Placement.** `position` (int) sets both the sort order and which section the
+item lands in - the core sidebar (`AppLayout.vue:buildNavItems`) assigns section
+headers by position range:
+
+| `position` | section |
+|-----------|---------|
+| `< 10` | top, above any header (Dashboard is 0, Map is 4) |
+| `10-29` | **Assets** |
+| `30-49` | **Information** |
+| `>= 50` | trailing, below Information |
+
+Lower number sorts higher within a section. An explicit `'section':
+'information'` forces the Information group regardless of position. Only these
+two named sections exist; a new section needs a core edit to `buildNavItems`.
+The **Displays** group (kiosk/TV links) is hardcoded in `AppLayout.vue`, not
+plugin-driven.
+
+`icon` is a string key mapped to a Lucide component core-side (same idea as
+`get_settings_cards`); an unknown key renders with no icon.
+
 > Removed in contract 0.4.0: `get_searchable_fields`. Global search
 > (`/api/search`) is a core concern that queries the asset model directly and
 > already covers every bundled asset type; no plugin ever implemented the hook.