feat(gateway): hivectl gateway user management + fix htpasswdFile assertion

Add `hivectl gateway {create-user,delete-user,list-users}` subcommands for
managing htpasswd files used by gateway Basic auth. Pure Rust bcrypt
(cost 12, $2y$ prefix nginx accepts). No external htpasswd binary required.

Also fix the NixOS module assertion: `cfg.auth ? htpasswdFile` is always
true in the module system (declared options always exist as keys); switch
to `nullOr path; default = null` + `!= null` check so the assertion
actually fires with a useful error when enable=true but no file is set.
Guard bind-mount and nginx config against null to prevent eval errors.

Update docs/gateway.md to show hivectl commands instead of raw htpasswd.

Cargo.lock

@@ -14,7 +14,7 @@ version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d122413f284cf2d62fb1b7db97e02edb8cda96d769b16e443a4f6195e35662b0"
 dependencies = [
- "crypto-common",
+ "crypto-common 0.1.7",
  "generic-array",
 ]
 
@@ -25,7 +25,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b169f7a6d4742236a0a00c541b845991d0ac43e546831af1249753ab4c3aa3a0"
 dependencies = [
  "cfg-if",
- "cipher",
+ "cipher 0.4.4",
  "cpufeatures 0.2.17",
 ]
 
@@ -303,6 +303,19 @@ version = "1.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2af50177e190e07a26ab74f8b1efbfe2ef87da2116221318cb1c2e82baf7de06"
 
+[[package]]
+name = "bcrypt"
+version = "0.19.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "24ae5479c93d3720e4c1dbd6b945b97457c50cb672781104768190371df1a905"
+dependencies = [
+ "base64",
+ "blowfish",
+ "getrandom 0.4.2",
+ "subtle",
+ "zeroize",
+]
+
 [[package]]
 name = "bitflags"
 version = "2.11.1"
@@ -350,12 +363,28 @@ dependencies = [
  "generic-array",
 ]
 
+[[package]]
+name = "blowfish"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "62ce3946557b35e71d1bbe07ec385073ce9eda05043f95de134eb578fcf1a298"
+dependencies = [
+ "byteorder",
+ "cipher 0.5.2",
+]
+
 [[package]]
 name = "bumpalo"
 version = "3.20.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72f5acc6cb2ba439de613abc23857ec3d78374d8ed5ac84e9d11336e87da8649"
 
+[[package]]
+name = "byteorder"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fd0f2584146f6f2ef48085050886acf353beff7305ebd1ae69500e27c67f64b"
+
 [[package]]
 name = "bytes"
 version = "1.11.1"
@@ -374,7 +403,7 @@ version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "26b52a9543ae338f279b96b0b9fed9c8093744685043739079ce85cd58f289a6"
 dependencies = [
- "cipher",
+ "cipher 0.4.4",
 ]
 
 [[package]]
@@ -406,7 +435,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c3613f74bd2eac03dad61bd53dbe620703d4371614fe0bc3b9f04dd36fe4e818"
 dependencies = [
  "cfg-if",
- "cipher",
+ "cipher 0.4.4",
  "cpufeatures 0.2.17",
 ]
 
@@ -418,7 +447,7 @@ checksum = "10cd79432192d1c0f4e1a0fef9527696cc039165d729fb41b3f4f4f354c2dc35"
 dependencies = [
  "aead",
  "chacha20",
- "cipher",
+ "cipher 0.4.4",
  "poly1305",
  "zeroize",
 ]
@@ -443,11 +472,21 @@ version = "0.4.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "773f3b9af64447d2ce9850330c473515014aa235e6a783b02db81ff39e4a3dad"
 dependencies = [
- "crypto-common",
- "inout",
+ "crypto-common 0.1.7",
+ "inout 0.1.4",
  "zeroize",
 ]
 
+[[package]]
+name = "cipher"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e8cf2a2c93cd704877c0858356ed03480ff301ee950b43f1cbe4573b088bfa6c"
+dependencies = [
+ "crypto-common 0.2.2",
+ "inout 0.2.2",
+]
+
 [[package]]
 name = "clap"
 version = "4.6.1"
@@ -591,6 +630,15 @@ dependencies = [
  "typenum",
 ]
 
+[[package]]
+name = "crypto-common"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ce6e4c961d6cd6c9a86db418387425e8bdeaf05b3c8bc1411e6dca4c252f1453"
+dependencies = [
+ "hybrid-array",
+]
+
 [[package]]
 name = "curve25519-dalek"
 version = "4.1.3"
@@ -742,7 +790,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9ed9a281f7bc9b7576e61468ba615a66a5c8cfdff42420a70aa82701a3b1e292"
 dependencies = [
  "block-buffer",
- "crypto-common",
+ "crypto-common 0.1.7",
  "subtle",
 ]
 
@@ -1200,6 +1248,7 @@ dependencies = [
  "anyhow",
  "axum",
  "base64",
+ "bcrypt",
  "clap",
  "hive-sh4re",
  "listenfd",
@@ -1353,6 +1402,15 @@ version = "1.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "df3b46402a9d5adb4c86a0cf463f42e19994e3ee891101b1841f30a545cb49a9"
 
+[[package]]
+name = "hybrid-array"
+version = "0.4.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9155a582abd142abc056962c29e3ce5ff2ad5469f4246b537ed42c5deba857da"
+dependencies = [
+ "typenum",
+]
+
 [[package]]
 name = "hyper"
 version = "1.10.1"
@@ -1618,6 +1676,15 @@ dependencies = [
  "generic-array",
 ]
 
+[[package]]
+name = "inout"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4250ce6452e92010fdf7268ccc5d14faa80bb12fc741938534c58f16804e03c7"
+dependencies = [
+ "hybrid-array",
+]
+
 [[package]]
 name = "ipnet"
 version = "2.12.0"
@@ -3740,7 +3807,7 @@ version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fc1de2c688dc15305988b563c3854064043356019f97a4b46276fe734c4f07ea"
 dependencies = [
- "crypto-common",
+ "crypto-common 0.1.7",
  "subtle",
 ]