Implement critical security improvements for authentication

This commit addresses several security vulnerabilities in the authentication
and authorization system:

1. JWT Encoding Panic Fix (Critical)
   - Replace .unwrap() with proper error handling in JWT token generation
   - Prevents server crashes from encoding failures
   - Returns HTTP 500 with error logging instead of panicking

2. Rate Limiting for Login Endpoint (Critical)
   - Add actix-governor dependency (v0.5)
   - Configure rate limiter: 2 requests/sec with burst of 5
   - Protects against brute-force authentication attacks

3. Strengthen Password Requirements
   - Minimum length increased from 6 to 12 characters
   - Require uppercase, lowercase, numeric, and special characters
   - Add comprehensive validation with clear error messages

4. Fix Token Parsing Vulnerability
   - Replace unsafe split().last().unwrap_or() pattern
   - Use strip_prefix() for proper Bearer token validation
   - Return InvalidToken error for malformed Authorization headers

5. Improve Authentication Logging
   - Sanitize error messages to avoid leaking user existence
   - Change from "User not found or incorrect password" to "Failed login attempt"

All changes tested and verified with existing test suite (65/65 tests passing).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Cargo.lock

@@ -82,6 +82,18 @@ dependencies = [
  "v_htmlescape",
 ]
 
+[[package]]
+name = "actix-governor"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a2e7b88f3804e01bd4191fdb08650430bbfcb43d3d9b2890064df3551ec7d25b"
+dependencies = [
+ "actix-http",
+ "actix-web",
+ "futures",
+ "governor",
+]
+
 [[package]]
 name = "actix-http"
 version = "3.11.1"
@@ -874,6 +886,19 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "dashmap"
+version = "5.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "978747c1d849a7d2ee5e8adc0159961c48fb7e5db2f06af6723b80123bb53856"
+dependencies = [
+ "cfg-if",
+ "hashbrown 0.14.5",
+ "lock_api",
+ "once_cell",
+ "parking_lot_core",
+]
+
 [[package]]
 name = "deranged"
 version = "0.5.3"
@@ -1218,6 +1243,12 @@ version = "0.3.31"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f90f7dce0722e95104fcb095585910c0977252f286e354b5e3bd38902cd99988"
 
+[[package]]
+name = "futures-timer"
+version = "3.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f288b0a4f20f9a56b5d1da57e2227c661b7b16168e2f72365f57b63326e29b24"
+
 [[package]]
 name = "futures-util"
 version = "0.3.31"
@@ -1277,6 +1308,26 @@ version = "0.31.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "07e28edb80900c19c28f1072f2e8aeca7fa06b23cd4169cefe1af5aa3260783f"
 
+[[package]]
+name = "governor"
+version = "0.6.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68a7f542ee6b35af73b06abc0dad1c1bae89964e4e253bc4b587b91c9637867b"
+dependencies = [
+ "cfg-if",
+ "dashmap",
+ "futures",
+ "futures-timer",
+ "no-std-compat",
+ "nonzero_ext",
+ "parking_lot",
+ "portable-atomic",
+ "quanta",
+ "rand 0.8.5",
+ "smallvec",
+ "spinning_top",
+]
+
 [[package]]
 name = "h2"
 version = "0.3.27"
@@ -1315,6 +1366,12 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.14.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5274423e17b7c9fc20b6e7e208532f9b19825d82dfd615708b70edd83df41f1"
+
 [[package]]
 name = "hashbrown"
 version = "0.15.5"
@@ -1610,6 +1667,7 @@ dependencies = [
  "actix",
  "actix-cors",
  "actix-files",
+ "actix-governor",
  "actix-multipart",
  "actix-rt",
  "actix-web",
@@ -1666,7 +1724,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f2481980430f9f78649238835720ddccc57e52df14ffce1c6f37391d61b563e9"
 dependencies = [
  "equivalent",
- "hashbrown",
+ "hashbrown 0.15.5",
 ]
 
 [[package]]
@@ -2018,6 +2076,12 @@ version = "1.0.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "650eef8c711430f1a879fdd01d4745a7deea475becfb90269c06775983bbf086"
 
+[[package]]
+name = "no-std-compat"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b93853da6d84c2e3c7d730d6473e8817692dd89be387eb01b94d7f108ecb5b8c"
+
 [[package]]
 name = "nom"
 version = "7.1.3"
@@ -2028,6 +2092,12 @@ dependencies = [
  "minimal-lexical",
 ]
 
+[[package]]
+name = "nonzero_ext"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38bf9645c8b145698bb0b18a4637dcacbc421ea49bef2317e4fd8065a387cf21"
+
 [[package]]
 name = "noop_proc_macro"
 version = "0.3.0"
@@ -2448,6 +2518,21 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "quanta"
+version = "0.12.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f3ab5a9d756f0d97bdc89019bd2e4ea098cf9cde50ee7564dde6b81ccc8f06c7"
+dependencies = [
+ "crossbeam-utils",
+ "libc",
+ "once_cell",
+ "raw-cpuid",
+ "wasi 0.11.1+wasi-snapshot-preview1",
+ "web-sys",
+ "winapi",
+]
+
 [[package]]
 name = "quick-error"
 version = "2.0.1"
@@ -2578,6 +2663,15 @@ dependencies = [
  "rgb",
 ]
 
+[[package]]
+name = "raw-cpuid"
+version = "11.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "498cd0dc59d73224351ee52a95fee0f1a617a2eae0e7d9d720cc622c73a54186"
+dependencies = [
+ "bitflags",
+]
+
 [[package]]
 name = "rayon"
 version = "1.11.0"
@@ -2919,6 +3013,15 @@ dependencies = [
  "windows-sys 0.59.0",
 ]
 
+[[package]]
+name = "spinning_top"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d96d2d1d716fb500937168cc09353ffdc7a012be8475ac7308e1bdf0e3923300"
+dependencies = [
+ "lock_api",
+]
+
 [[package]]
 name = "stable_deref_trait"
 version = "1.2.0"
@@ -3546,6 +3649,22 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "winapi"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
 [[package]]
 name = "winapi-util"
 version = "0.1.10"
@@ -3555,6 +3674,12 @@ dependencies = [
  "windows-sys 0.60.2",
 ]
 
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
+
 [[package]]
 name = "windows-core"
 version = "0.61.2"