stacks: remove 9 folders, update stack count in README

Removed: ollama (AI-related concerns), emby/qbittorrent/prowlarr
(media-download concerns), bookstack (being deprecated in the
homelab), and mariadb-latest/mysql-8/postgres-18-alpine/valkey-9.0-
alpine (build-only base-image factories - nothing connects to them,
they add no portfolio value on their own; real per-app DB usage,
e.g. Kodi's own mariadb service, already lives in that app's stack
folder and is unaffected).

Stack count updated 53 -> 44 in both README references.

README.md

@@ -13,7 +13,7 @@
 <table style="margin: 0 auto;">
 <tr>
 <td align="center">🖥️<br/><strong style="font-size:1.6em;">11</strong><br/>fleet hosts</td>
-<td align="center">🐳<br/><strong style="font-size:1.6em;">53</strong><br/>compose stacks</td>
+<td align="center">🐳<br/><strong style="font-size:1.6em;">44</strong><br/>compose stacks</td>
 <td align="center">📚<br/><strong style="font-size:1.6em;">15</strong><br/>documented systems</td>
 <td align="center">🧱<br/><strong style="font-size:1.6em;">4</strong><br/>trust boundaries</td>
 <td align="center">🔁<br/><strong style="font-size:1.6em;">13</strong><br/>automated maintenance flows</td>
@@ -112,7 +112,7 @@ Authentik, self-hosted, fronts single sign-on fleet-wide — native OIDC where a
 
 ## What's Running
 
-53 Docker Compose stacks, grouped by purpose rather than by which host happens to run them — see [`stacks/`](stacks/): identity & security, platform/infra, media, productivity, and dev tools.
+44 Docker Compose stacks, grouped by purpose rather than by which host happens to run them — see [`stacks/`](stacks/): identity & security, platform/infra, media, productivity, and dev tools.
 
 ---