puppet::migrate: drive k8s cutover from a single enabled boolean

Wire profiles::puppet::migrate into profiles::base (shipping enabled=>false)
so every node evaluates it. client.pp now includes migrate and folds
new_server/new_ca_server/new_ssldir into the effective server/ca_server/
report_server/ssldir it renders, so flipping the one
profiles::puppet::migrate::enabled key at any hiera layer (node/role/common)
repoints a target -- no per-node client param overrides.

Explicit client::ssldir/::report_server still override the migrate-derived
value; unmigrated nodes render a byte-identical puppet.conf.

site/profiles/manifests/puppet/migrate.pp

@@ -21,48 +21,45 @@
 # NOTE: this is deliberately hiera-driven per node/role so waves can be rolled
 # out and rolled back one target at a time. The class only manages the fresh
 # ssldir; the actual puppet.conf changes ride on profiles::puppet::client's
-# existing template via its $server / $ca_server / $report_server / $ssldir
-# params (see the hiera block below). Do NOT add a second File resource for
-# puppet.conf here -- client.pp already owns it.
+# existing template. client.pp `include`s this class and, when enabled, folds
+# new_server / new_ca_server / new_ssldir into the effective server /
+# ca_server / report_server / ssldir it renders. Do NOT add a second File
+# resource for puppet.conf here -- client.pp already owns it.
 #
-# == Wiring (hiera_include convention)
+# == Wiring (single boolean)
 #
-# This class is opt-in via hiera_include; it is not pulled in by
-# profiles::base. To migrate a target add the class to hiera_include AND flip
-# the client params so puppet.conf carries the new endpoints + fresh ssldir.
+# This class ships wired into profiles::base with enabled => false, so every
+# node evaluates it but nothing changes until the boolean is flipped. Because
+# client.pp includes it and reads its params, setting the ONE key below at any
+# hiera layer repoints a target -- no client.pp param overrides needed.
+#
+# The endpoints (new_server / new_ca_server / new_ssldir) are param defaults
+# on this class; override them in hiera too if the k8s names ever change.
 #
 # --- Canary: one node -> hieradata/nodes/<certname>.yaml -------------------
-#   hiera_include:
-#     - profiles::puppet::migrate
-#
 #   profiles::puppet::migrate::enabled: true
-#
-#   # repoint the agent (client.pp owns puppet.conf; migrate.pp owns ssldir)
-#   profiles::puppet::client::server: 'puppet.k8s.syd1.au.unkin.net'
-#   profiles::puppet::client::ca_server: 'puppetca.k8s.syd1.au.unkin.net'
-#   profiles::puppet::client::report_server: 'puppet.k8s.syd1.au.unkin.net'
-#   profiles::puppet::client::ssldir: '/etc/puppetlabs/puppet/ssl-k8s'
 # ---------------------------------------------------------------------------
 #
 # --- Wave: a whole role -> hieradata/roles/<t1>/<t2>[/<t3>].yaml -----------
-#   (same keys as the canary block above)
+#   profiles::puppet::migrate::enabled: true
 # ---------------------------------------------------------------------------
 #
-# --- Final flip: hieradata/common.yaml (retires the legacy masters) --------
-#   profiles::puppet::client::server: 'puppet.k8s.syd1.au.unkin.net'
-#   profiles::puppet::client::ca_server: 'puppetca.k8s.syd1.au.unkin.net'
-#   profiles::puppet::client::report_server: 'puppet.k8s.syd1.au.unkin.net'
-#   profiles::puppet::client::ssldir: '/etc/puppetlabs/puppet/ssl-k8s'
-#   # profiles::puppet::migrate no longer needs to be in hiera_include once the
-#   # fleet default points at k8s and the fresh ssldir exists everywhere.
+# --- Estate flip -> hieradata/common.yaml (retires the legacy masters) -----
+#   profiles::puppet::migrate::enabled: true
 # ---------------------------------------------------------------------------
 #
+# Manual override: profiles::puppet::client::ssldir and ::report_server are
+# Optional and, when set explicitly in hiera, win over the migrate-derived
+# value. server / ca_server have no undef sentinel, so while enabled => true
+# the migrate endpoints win; to point a target at a bespoke server leave
+# enabled => false for it and set profiles::puppet::client::server directly.
+#
 # == Rollback (per target)
 #
-# Delete the migration block from the node/role hiera (or set the client keys
-# back to the legacy values and drop the ssldir override). The next run
-# rewrites puppet.conf back to the legacy ssldir, which still contains the
-# original CA-signed cert, and the node is back on the VM masters.
+# Remove the profiles::puppet::migrate::enabled key (or set it back to false)
+# at the node/role/common layer. The next run rewrites puppet.conf back to the
+# legacy server + legacy ssldir, which still contains the original CA-signed
+# cert, and the node is back on the VM masters.
 #
 # site/profiles/manifests/puppet/migrate.pp
 class profiles::puppet::migrate (