feat(fleet): export a whole-fleet Markdown dossier (#1334)

* feat(fleet): export a whole-fleet Markdown dossier

Add an admin-only "Export Dossier" action to the Fleet view that walks
every node and stack, pairs each stack's generated Compose anatomy with
its operator notes, and downloads a folder-structured homelab-dossier.zip
(index, per-node and per-stack pages, plus fleet-wide port, volume,
network, env, access-URL, and VLAN/firewall maps).

Reuses the existing stack dossier and anatomy Markdown generators by
extracting the shared Compose parsers into a frontend lib module.
Unreachable nodes are recorded with a reason and never block the export;
only env variable names and counts are ever emitted, never values.

* fix(fleet): unique stack slugs and reproducible dossier archive

Disambiguate stack names on one node that slugify to the same value (e.g.
`Web` and `web` on a case-sensitive host) with a per-node slug map shared by
the node-page links and the file emission, so neither overwrites the other.
Pin a fixed entry timestamp on the zip so the archive bytes are a pure
function of the file map rather than the wall clock.

docs/docs.json

@@ -141,6 +141,7 @@
                   "features/pilot-agent",
                   "features/sencho-mesh",
                   "features/fleet-view",
+                  "features/fleet-dossier",
                   "features/fleet-federation",
                   "features/fleet-actions",
                   "features/fleet-sync",