Generate a v0.16 apply plan for the listeners migrate_v016.py leaves behind

First piece of ARCHITECTURE.md 4.3's apply-plan, and the piece that decides
whether a migrated server answers at all: server.listener is not among the
settings the official converter carries, so a freshly migrated instance
binds nothing. Every other unmigrated setting degrades the server; this one
stops it being a server.

internal/applyplan maps server.listener.* onto x:NetworkListener objects and
reports its own coverage. Against the smoke instance that is 24 of 3,505
unmigrated keys - 0.7% - and the output says 0.7%, listing the largest
groups it did not touch. A plan covering a fraction while implying
completeness would be worse than no plan.

The wire format was confirmed against the binary, not the documentation.
The published schema reference gives NetworkListener.bind as a JSON array;
0.16.14 rejects that outright ("Invalid value for object property.
Properties: bind"). The encoding it accepts is a value-keyed set,
{"[::]:25": true}, found by applying a plan to a live recovery-mode 0.16.14
and reading it back with `stalwart-cli snapshot`. Only mappings confirmed
that way are in DefaultGenerators; managesieve -> manageSieve is the one
protocol whose spelling changes, and an unrecognized protocol is reported
and skipped rather than passed through to fail at apply time.

Operations are upserts matched on name, so a plan can be re-run - an
operator will run it more than once - and the supplement is applied after
export.json rather than merged into it, so a generated mapping can never
override one the official script got right.

Verified end to end: rehearse against a real 0.15.5 generated ten
listeners, `stalwart-cli apply` created all ten on a real 0.16.14 with zero
failures, a snapshot read them back with correct protocols, binds and TLS
flags, and re-applying reported 10 updated / 0 created / 0 failed.

README.md

@@ -112,6 +112,18 @@ It copies no data, clones nothing, starts no server, and never writes to the
 store, so it is safe to run against production repeatedly and without a
 maintenance window.
 
+It also generates a **supplemental plan** for the part it can rebuild
+automatically — currently your network listeners, which is the difference
+between a migrated server that answers and one that doesn't — and reports
+exactly how much of the worklist that covers (on a test instance: 24 of
+3,505 keys, and it says so rather than implying more). Review it, then apply
+it after `export.json`:
+
+```sh
+stalwart-cli apply --file <state-dir>/runs/<run-id>/supplement.json \
+    --url https://mail.example.com
+```
+
 Expect the worklist to be long. Measured against a real production instance,
 `migrate_v016.py` carried **219 of 12,401 settings — 1.8%**. The rest,
 including `server.listener`, has to be rebuilt by hand; until it is, a