fix: port the PR #6105 review-round fixes into this fork's own AmneziaWG code

Same 8 findings fixed on upstream-pr/amneziawg, ported here since this
fork's internal/amneziawg + related web/service files predate that PR
branch's own fix-up commits:

1. hostRulesFingerprint now folds in a peer's IPv4 whenever
   ForwardedPorts is set, not only when RouteThroughXray is on, so a
   re-IP forces the bounce needed to move the DNAT rule too.
2. ValidateConfigValue (new, params.go) rejects control characters in
   server/client keys, email and I1 at save time; sanitizeConfigValue
   strips them defensively at .conf-render time.
3. checkForwardedPortsConflict now scopes to node_id IS NULL and takes
   a pre-loaded portConflictContext (loadPortConflictContext), so a
   port used only on another node isn't a false collision and an
   inbound with N clients costs one query instead of N.
4. PostDown commands are now best-effort (appendOrTrue) so an external
   firewall flush can't abort the rest of the teardown chain.
5. The "ip rule list | grep -q" existence check now uses
   grep -c >/dev/null, avoiding a pipefail/SIGPIPE false negative that
   could re-add a duplicate rule.
6. route_egress.go's stale "always present, no opt-in" comment
   corrected to describe the real RouteThroughXray-gated behavior.
   (This fork's genAmneziaWGLink already emits vpn://, and there's no
   upstream-facing docs page here, so neither needed the PR branch's
   Finding 6 docs/link-format changes.)
7. install.sh: Arch's ndppd install uses pacman -Sy, not -Syu, matching
   every other pacman call in the script; should_install_amneziawg
   short-circuits to yes when awg is already installed, so `x-ui
   update` doesn't re-prompt -- this fork's own opt-out-by-default
   philosophy for should_install_amneziawg is unchanged, only the
   redundant-reprompt behavior is fixed.
8. CollectTraffic checks pointer identity before writing back a
   traffic-counter baseline, so a concurrent restart's freshly-reset
   (empty) baseline can't be clobbered by stale pre-restart counters.
   sweepOrphansLocked no longer permanently disables itself on a
   transient os.ReadDir failure.

go build/vet/test and frontend typecheck/lint/build/vitest all pass.

internal/amneziawg/params.go

@@ -189,6 +189,25 @@ func ValidateSubnetIPv4(subnetIP string, subnetCIDR int) error {
 	return nil
 }
 
+// ValidateConfigValue rejects a value containing a newline, carriage return,
+// or other control character before it's saved. PrivateKey/PublicKey/I1 on
+// the server block, and Email/PublicKey/PreSharedKey per client, all get
+// interpolated verbatim into the generated .conf by generateServerConfig; a
+// newline in any of them lets a later line re-open a new [Interface]/[Peer]
+// section, and awg-quick's parser collects a following "PostUp = ..." line
+// into a hook it executes as root on the next apply — the same class this
+// package already closes for ExternalInterface/IPv6ExternalInterface (see
+// ValidateInterfaceName) and SubnetIP (see ValidateSubnetIPv4). field names
+// the value in the returned error, e.g. "email" or "publicKey".
+func ValidateConfigValue(field, v string) error {
+	for _, r := range v {
+		if r == '\n' || r == '\r' || r < 0x20 || r == 0x7f {
+			return fmt.Errorf("invalid %s: control characters are not allowed", field)
+		}
+	}
+	return nil
+}
+
 // validateHValue checks one H parameter: empty, a single uint32, or
 // "low-high" with 0 <= low <= high <= uint32 max.
 func validateHValue(v string) error {