feat(stacks): add Stack Dossier tab with operator notes and Markdown export (#1326)

* feat(stacks): add Stack Dossier tab with operator notes and Markdown export

Add a Dossier tab beside Anatomy and Activity on the stack detail panel. It
shows a read-only summary auto-derived from the stack's Compose anatomy
(services, ports, volumes, network, restart policy, env file, source) plus an
editable form for the context Sencho cannot infer: purpose, owner, access URLs,
static IP, VLAN, and firewall, reverse-proxy, backup, upgrade, recovery, and
custom notes.

Notes persist per stack and per node in a new stack_dossiers table, reached
transparently through the remote-node proxy so a remote stack's dossier
round-trips to the node that owns it. Reading a dossier needs stack read
permission; saving needs stack edit. The tab exports a single Markdown document
combining the generated facts and the operator notes, with copy-to-clipboard and
download actions; env values are never exported, only variable names and counts.

Available on all tiers. The standalone anatomy copy-as-Markdown shortcut is
removed since the Dossier export supersedes it.

* fix(stacks): gate dossier reads/writes on stack existence; clear dossier on node delete

A dossier endpoint validated the stack name but not that the stack exists, so an
editor could PUT a dossier for a name with no stack, leaving an orphan row that a
later stack of the same name would inherit. Require the stack to exist (existing
requireStackExists guard) on the dossier GET and PUT, returning 404 otherwise.

Also clear a node's stack_dossiers rows when the node is deleted, alongside the
other node-scoped cleanup, so removing a node leaves no orphan dossiers.

Docs: scope the "no secret exported" statement to the generated facts (which only
ever carry variable names and counts) and clarify that operator notes are
exported exactly as written.

docs/docs.json

@@ -103,6 +103,7 @@
                   "features/editor",
                   "features/stack-file-explorer",
                   "features/stack-activity",
+                  "features/stack-dossier",
                   "features/stack-labels",
                   "features/sidebar"
                 ]