backend: add user management system with SQLite database

Add authentication and authorization infrastructure:
- SQLite database (db.rs) with users, sessions, and app permissions tables
- Password hashing with argon2
- Session-based auth with random 256-bit tokens
- Auth middleware (session validation) and admin middleware
- Login/logout/me endpoints
- Admin CRUD endpoints for user and permission management
- Auto-seed default admin user on first run
- 23 unit tests covering all DB operations

Existing API endpoints are not yet gated behind auth.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Cargo.lock

@@ -93,6 +93,18 @@ version = "1.0.98"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e16d2d3311acee920a9eb8d33b8cbc1787ce4a264e85f964c2404b969bdcd487"
 
+[[package]]
+name = "argon2"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3c3610892ee6e0cbce8ae2700349fcf8f98adb0dbfbee85aec3c9179d29cc072"
+dependencies = [
+ "base64ct",
+ "blake2",
+ "cpufeatures",
+ "password-hash",
+]
+
 [[package]]
 name = "arrayvec"
 version = "0.7.6"
@@ -143,6 +155,12 @@ version = "0.22.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
 
+[[package]]
+name = "base64ct"
+version = "1.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2af50177e190e07a26ab74f8b1efbfe2ef87da2116221318cb1c2e82baf7de06"
+
 [[package]]
 name = "bindgen"
 version = "0.72.0"
@@ -181,6 +199,15 @@ dependencies = [
  "wyz",
 ]
 
+[[package]]
+name = "blake2"
+version = "0.10.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "46502ad458c9a52b69d4d4d32775c788b7a1b85e8bc9d482d92250fc0e3f8efe"
+dependencies = [
+ "digest",
+]
+
 [[package]]
 name = "block-buffer"
 version = "0.10.4"
@@ -531,6 +558,18 @@ dependencies = [
  "xxhash-rust",
 ]
 
+[[package]]
+name = "fallible-iterator"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2acce4a10f12dc2fb14a218589d4f1f62ef011b2d0cc4b3cb1bba8e94da14649"
+
+[[package]]
+name = "fallible-streaming-iterator"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7360491ce676a36bf9bb3c56c1aa791658183a54d2744120f27285738d90465a"
+
 [[package]]
 name = "fastrand"
 version = "2.3.0"
@@ -553,6 +592,12 @@ version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
 
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
 [[package]]
 name = "foreign-types"
 version = "0.3.2"
@@ -677,6 +722,7 @@ name = "gamestream-webtransport-proxy"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "argon2",
  "directories",
  "flatbuffers",
  "getrandom 0.3.3",
@@ -690,6 +736,7 @@ dependencies = [
  "openssl",
  "rand 0.9.1",
  "reqwest",
+ "rusqlite",
  "salvo",
  "serde",
  "serde-xml-rs",
@@ -834,6 +881,18 @@ name = "hashbrown"
 version = "0.15.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5971ac85611da7067dbfcabef3c70ebb5606018acd9e2a3903a0da507521e0d5"
+dependencies = [
+ "foldhash",
+]
+
+[[package]]
+name = "hashlink"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7382cf6263419f2d8df38c55d7da83da5c18aef87fc7a7fc1fb1e344edfe14c1"
+dependencies = [
+ "hashbrown 0.15.4",
+]
 
 [[package]]
 name = "headers"
@@ -1256,6 +1315,17 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "libsqlite3-sys"
+version = "0.32.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fbb8270bb4060bd76c6e96f20c52d80620f1d82a3470885694e41e0f81ef6fe7"
+dependencies = [
+ "cc",
+ "pkg-config",
+ "vcpkg",
+]
+
 [[package]]
 name = "linux-raw-sys"
 version = "0.9.4"
@@ -1549,6 +1619,17 @@ dependencies = [
  "windows-targets 0.52.6",
 ]
 
+[[package]]
+name = "password-hash"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "346f04948ba92c43e8469c1ee6736c7563d71012b17d40745260fe106aac2166"
+dependencies = [
+ "base64ct",
+ "rand_core 0.6.4",
+ "subtle",
+]
+
 [[package]]
 name = "path-slash"
 version = "0.2.1"
@@ -1989,6 +2070,20 @@ dependencies = [
  "syn 1.0.109",
 ]
 
+[[package]]
+name = "rusqlite"
+version = "0.34.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37e34486da88d8e051c7c0e23c3f15fd806ea8546260aa2fec247e97242ec143"
+dependencies = [
+ "bitflags",
+ "fallible-iterator",
+ "fallible-streaming-iterator",
+ "hashlink",
+ "libsqlite3-sys",
+ "smallvec",
+]
+
 [[package]]
 name = "rust-embed"
 version = "8.6.0"