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/features/stack-dossier.mdx

@@ -52,6 +52,8 @@ Two actions in the tab header produce a single Markdown document combining the g
 
 The export is clean Markdown that reads well in Git, Obsidian, BookStack, a README, or stored alongside a backup. The generated facts never include `.env` values, only variable names and counts. Your operator notes are exported exactly as you write them, so treat them like any document you might share and avoid pasting secrets you do not want in the export.
 
+To export every stack across every node at once, use the [Fleet Dossier](/features/fleet-dossier) action in the Fleet view.
+
 ## Accessing the Dossier tab
 
 1. Click any stack in the left sidebar to open it.