fix(amneziawg): bound S1-S3 by the receive buffer, reject overlapping H (#6642)

* fix(amneziawg): bound S1-S3 by the receive buffer, reject overlapping H

The native AmneziaWG validator, both Zod schemas, both forms and the docs now
follow the rules amneziawg-go actually enforces.

S1-S3. A padded handshake message is 148+S1, 92+S2 or 64+S3 bytes
(device/send.go). The peer reads each datagram into a [MaxMessageSize]byte
buffer, where MaxMessageSize = MaxSegmentSize (device/pools.go,
constants.go). MaxSegmentSize is 65535 on Linux/Android, 2016 on Windows and
1700 on iOS (device/queueconstants_*.go). The limits are therefore
S1 <= 1552, S2 <= 1608 and S3 <= 1636. Before, S1/S2 allowed 65535, which
iOS peers silently drop, and S3 was capped at 64, a number inherited from the
coinman-dev/3ax-ui port in #6105 with no stated reason. That cap blocked real
configs such as Amnezia Premium's S3=1045. RandomTrailers only tops a packet
up to 500 bytes (DefaultUdpWindow), so it never pushes a message past these
limits.

H1-H4. amneziawg-go refuses the whole device when the header ranges overlap
("headers must not overlap", device/uapi.go mergeWithDevice), and so does the
kernel module (src/netlink.c). The panel did not check this, so an inbound
with overlapping ranges saved and then failed to apply. A blank H is never
sent, so the engine keeps its default, WireGuard's own type 1-4; the check
treats blank fields that way. The docs said 1-4 "must not be used". They are
valid and are the engine default, only unobfuscated without a
HeaderProtectionKey. The docs also said amneziawg-go rejects S1+56 == S2. It
does not (IpcSet accepts it). The panel keeps that rule as a fingerprint
guard, and the docs now say so.

Tests: the new params_test cases and the Zod bounds fail on the old code.
TestValidatedObfuscationAlwaysApplies runs every accepted set through a real
amneziawg-go IpcSet and now covers overlap, blank-H defaults, H=1-4, the
exact S bounds and the full Amnezia Premium set. Before this fix it failed
with "headers must not overlap".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* fix(amneziawg): bound only inbound padding by the iOS receive buffer

The 1700-byte iOS buffer limits what an inbound's clients can receive,
but ValidateObfuscation also runs for outbounds, and the Xray template
save re-validates every AmneziaWG outbound. An outbound whose remote
server uses S1 above 1552 would have blocked every Xray settings save,
though its values come from that server and are received on Linux.

ValidateObfuscation keeps amneziawg-go's uint16 UAPI width for S1-S3;
ValidateServerObfuscation adds the receive-buffer bounds and is what
inbounds call. The outbound schema and form follow the same split.

---------

Co-authored-by: Kirill Rudenko <rudenko@npp-energy.ru>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Sanaei <ho3ein.sanaei@gmail.com>

docs/content/docs/en/config/amneziawg.mdx

@@ -43,10 +43,10 @@ value defeats the point, since DPI can fingerprint it over time.
 | ------------ | ---------------------------------------------------------------------------- |
 | **Jc**       | Number of junk packets sent before the handshake.                            |
 | **Jmin/Jmax** | Size range (bytes) for those junk packets. `Jmin` must not exceed `Jmax`.     |
-| **S1/S2**    | Padding added to the handshake init/response packets. `S1 + 56` must not equal `S2` — amneziawg-go rejects a value that would make both packets the same size. |
-| **S3**       | Cookie-reply padding, `0`-`64`.                                               |
+| **S1/S2**    | Padding added to the handshake init/response packets, `0`-`1552` / `0`-`1608`: the packets are `148 + S1` and `92 + S2` bytes and must fit the 1700-byte receive buffer amneziawg-go uses on iOS. The panel also rejects `S1 + 56 = S2`, which would give both packets the same size on the wire (amneziawg-go itself accepts it). An AmneziaWG outbound takes the remote server's values as they are, up to `65535`. |
+| **S3**       | Cookie-reply padding, `0`-`1636`: the reply is `64 + S3` bytes and must fit the 1700-byte receive buffer amneziawg-go uses on iOS. An outbound, as with S1/S2, takes the remote server's value up to `65535`. |
 | **S4**       | Transport (data) packet padding, `0`-`32`.                                    |
-| **H1-H4**    | Magic header values that replace WireGuard's standard message-type bytes. Each is a single integer or a `low-high` range; `1`-`4` are reserved (real WireGuard message types) and must not be used. |
+| **H1-H4**    | Header values that replace WireGuard's message-type field. Each is a single integer or a `low-high` range, and the four must not overlap — amneziawg-go and the kernel module refuse the whole device otherwise. `1`-`4` are WireGuard's own types and the engine default for a blank field: valid, but without a HeaderProtectionKey the type field then reads like plain WireGuard. |
 | **I1-I5**    | Optional signature packets — random bytes prepended before the handshake, e.g. `<r 148>`. Generated sets fill `I1` only, matching Amnezia's own generator. |
 | **HeaderProtectionKey** | A base64 32-byte key for the 3.0 header-protection mechanism. Must match on every client config; blank disables it. |
 | **ContentPaddingAddition** | A single integer or `low-high` byte range of extra padding on content packets. Kept `<= 64` by the generator so a 1420-MTU tunnel doesn't fragment. |