desktops: drop line numbers from the lifecycle code blocks

The mkdocs config enables linenums globally for every fenced
code block via pymdownx.highlight, which doubled up with the
inline '1. 2. 3.' step prefixes inside the install / remove /
upgrade-downgrade lifecycle blocks. The result was a left
gutter of 1..N alongside the inline 1. 2. 3. on every line —
two parallel numbering systems competing for attention.

Override per-block with `{ .text linenums="0" }` on the three
lifecycle code fences. The inline step numbers are the
canonical step IDs (referenced from the prose around them);
the auto gutter was redundant.

Other code blocks in the doc keep the global gutter — only
the lifecycle ascii-art blocks change.

Author: igorpecovnik

docs/Developer-Guide_Desktops.md

@@ -587,7 +587,7 @@ Not called from the desktop install path by default. The `armbian-imager` AppIma
 
 The install pipeline in `module_desktops install` is intentionally linear and idempotent-friendly. **Every step that touches system state is gated on the previous step's success.**
 
-```text
+```{ .text linenums="0" }
 1.  Validate args                 de= and tier= both required; tier must be minimal|mid|full
 2.  Resolve target user           module_desktop_getuser
 3.  Parse YAML at target tier     module_desktop_yamlparse $de $arch $release $tier
@@ -617,7 +617,7 @@ If step 10 or 11 fails, the function returns 1 with no further state changes —
 
 ## Lifecycle: remove
 
-```text
+```{ .text linenums="0" }
 1.  Validate args                 de= required
 2.  Read installed tier marker    /etc/armbian/desktop/<de>.tier (default: minimal)
 3.  Parse YAML at the installed   module_desktop_yamlparse $de $arch $release $installed_tier
@@ -640,7 +640,7 @@ The `set-default` and `isolate` calls together ensure the user gets a console lo
 
 `upgrade` and `downgrade` are the two halves of `_module_desktops_change_tier`:
 
-```text
+```{ .text linenums="0" }
 1.  Validate args                 de= and tier= required; tier must be minimal|mid|full
 2.  Read current tier marker      /etc/armbian/desktop/<de>.tier (must exist)
 3.  Validate direction            upgrade refuses target <= current