Move the `wg_lan` examples under `examples/multihost/`

`tests/test_docs_examples.py` walks `examples/` **recursively**
and subproc-runs every collected file asserting `rc == 0`. Ran
its exact filter against the tree: all 4 of our files were being
collected — including `README.md`, since the filter never checks
the extension, so CI would have literally tried `python
README.md`. These need a real second host + a live `wg` tunnel,
so they can't ever satisfy that gate.

`'multihost' not in p[0]` is already in the test's exclusion
list w/ no dir yet using it, so this is a pure `git mv` — zero
test changes — and it's what the exclusion was plainly there
for. Collection drops 24 -> 20 files, 0 of them ours.

Also records *why* in the two places someone would look before
adding the next one: a callout at the top of the example README
and a note on plan 03's §3.4 deliverables. Anything needing a
second host or live tunnel goes under `examples/multihost/`.

(this patch was generated in some part by `claude-code` using `claude-opus-5` (`anthropic`))

ai/tpt-backends/03_wg_tunnel_bindspace.md

@@ -134,7 +134,8 @@ examples in gh #482) used a *suffix* form
 semantically inverted: it puts the overlay addr where the bearer
 belongs, `tcp` where wg's `udp` `ListenPort` goes, and declares
 no overlay endpoint at all. `parse_wg_maddr()` in
-`examples/wg_lan/` now rejects it with an actionable error.
+`examples/multihost/wg_lan/` now rejects it with an actionable
+error.
 Observed protocol-name lists, for writing the `match`:
 
 | maddr | `[p.name for p in m.protocols()]` |
@@ -197,7 +198,14 @@ side-effect-free; verification is the *caller's* explicit step
 ### 3.4 deliverables
 
 - `examples/` scripts distilled from #482 §§3-5 (this is the
-  unchecked "commit examples from ^" bullet in #443).
+  unchecked "commit examples from ^" bullet in #443). They live
+  under `examples/multihost/` — `test_docs_examples.py` walks
+  `examples/` recursively and runs every collected file as a
+  subproc asserting `rc == 0` (it doesn't even filter by
+  extension, so a stray `README.md` would be `python`-run too),
+  and `'multihost' not in p[0]` is already in its exclusion
+  list. Anything needing a real second host or a live tunnel
+  belongs there.
 - a `docs/` page: tunnel setup, the maddr form, the two-host
   run. Keep prose in the docs; keep the examples runnable and
   minimal.

examples/multihost/wg_lan/README.md

@@ -8,6 +8,13 @@ Supersedes the example set in gh
 [#482](https://github.com/goodboy/tractor/issues/482) — see
 [what changed](#what-changed-vs-482).
 
+> **Why `examples/multihost/`?** `tests/test_docs_examples.py`
+> walks `examples/` recursively and runs everything it collects
+> as a subproc, asserting `rc == 0`. These need a real second
+> host and a live `wg` tunnel, so they can't satisfy that;
+> `'multihost' not in p[0]` is already in the test's exclusion
+> list, which is what keeps them out of CI.
+
 ## the maddr form
 
 ```