fix(amneziawg): H1-H4 generator + queue-depth throughput fixes (#6330)

* fix(amneziawg): stop H1-H4 generator misclassifying transport packets

Both the Go generator and its frontend mirror picked a random *range*
per H1-H4 field with only a minimum width enforced (no maximum).
amneziawg-go's packet classifier only ever compares a fixed-size
ciphertext prefix against these bounds, so a wide range buys no DPI
resistance -- the boundaries themselves are never observable on the
wire. It does cost real throughput: with randomTrailers on (the
default here), the handshake-size checks relax from == to >, so a
wide H-range misclassifies a proportional fraction of ordinary
transport packets as handshakes and silently drops them
(amnezia-vpn/amneziawg-go#183). A single value per field is strictly
safer than any range, with no obfuscation trade-off.

Live-tested: narrowing H1-H4 alone took AmneziaWG upload from
2-3 Mbit/s to 200+ Mbit/s on one box, and ~20 Mbit/s to 120-156 Mbit/s
on another, single-variable, no other change.

* fix(amneziawgnet): raise tunQueueDepth to absorb slow-start bursts

1024 was sized for a single-connection buffering problem (the
gVisor-to-amneziawg-go TUN handoff channel needing slack for the
download direction). tcpip.Stack.Stats() during a real many-connection
download (20-28 concurrent TCP flows, e.g. a segmented speed test)
showed SlowStartRetransmits jump by ~770 in a single second the moment
CurrentEstablished crossed ~20 -- consistent with many connections'
simultaneous slow-start growth briefly exceeding 1024 outstanding
packets and gVisor treating the resulting silent drops as real network
loss.

* fix(amneziawg): trim comment blocks to the repo's 2-line cap

Review feedback: four comment blocks in the previous commits exceeded
CLAUDE.md's 2-line-per-block hard rule (up to 13 lines). Trimmed each to
the one non-obvious fact plus the amneziawg-go#183 reference; the fuller
rationale already lives in the commit message. Also refreshed the stale
H1-H4 range example in docs/content/docs/en/config/amneziawg.mdx to match
the new single-value generator output.

internal/amneziawgnet/netstack.go

@@ -24,7 +24,8 @@ import (
 )
 
 // tunQueueDepth is the outbound queue depth for channel endpoint and handoff.
-const tunQueueDepth = 1024
+// 1024 starved simultaneous TCP slow-starts; channel.Endpoint drops silently when full.
+const tunQueueDepth = 8192
 
 // stackTun implements amneziawg-go tun.Device over a gVisor channel endpoint,
 // exposing *stack.Stack for forwarder attachment.