feat: add Keycloak authentication for dashboard and API endpoints (#2)

Dashboard: OAuth2/OIDC login flow with PKCE, session-based auth middleware
protecting all server function endpoints, check-auth server function for
frontend auth state, login page gate in AppShell, user info in sidebar.

Agent API: JWT validation middleware using Keycloak JWKS endpoint,
conditionally enabled when KEYCLOAK_URL and KEYCLOAK_REALM are set.

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

Co-authored-by: Sharang Parnerkar <parnerkarsharang@gmail.com>
Reviewed-on: #2

Cargo.lock

@@ -555,6 +555,7 @@ dependencies = [
  "git2",
  "hex",
  "hmac",
+ "jsonwebtoken",
  "mongodb",
  "octocrab",
  "regex",
@@ -595,6 +596,7 @@ name = "compliance-dashboard"
 version = "0.1.0"
 dependencies = [
  "axum",
+ "base64",
  "chrono",
  "compliance-core",
  "dioxus",
@@ -605,14 +607,19 @@ dependencies = [
  "dotenvy",
  "gloo-timers",
  "mongodb",
+ "rand 0.9.2",
  "reqwest",
  "secrecy",
  "serde",
  "serde_json",
+ "sha2",
  "thiserror 2.0.18",
+ "time",
  "tokio",
  "tower-http",
+ "tower-sessions",
  "tracing",
+ "url",
  "web-sys",
 ]
 
@@ -792,7 +799,12 @@ version = "0.18.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4ddef33a339a91ea89fb53151bd0a4689cfce27055c291dfa69945475d22c747"
 dependencies = [
+ "base64",
+ "hmac",
  "percent-encoding",
+ "rand 0.8.5",
+ "sha2",
+ "subtle",
  "time",
  "version_check",
 ]
@@ -5228,6 +5240,22 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "tower-cookies"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "151b5a3e3c45df17466454bb74e9ecedecc955269bdedbf4d150dfa393b55a36"
+dependencies = [
+ "axum-core",
+ "cookie",
+ "futures-util",
+ "http",
+ "parking_lot",
+ "pin-project-lite",
+ "tower-layer",
+ "tower-service",
+]
+
 [[package]]
 name = "tower-http"
 version = "0.6.8"
@@ -5268,6 +5296,57 @@ version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8df9b6e13f2d32c91b9bd719c00d1958837bc7dec474d94952798cc8e69eeec3"
 
+[[package]]
+name = "tower-sessions"
+version = "0.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "518dca34b74a17cadfcee06e616a09d2bd0c3984eff1769e1e76d58df978fc78"
+dependencies = [
+ "async-trait",
+ "http",
+ "time",
+ "tokio",
+ "tower-cookies",
+ "tower-layer",
+ "tower-service",
+ "tower-sessions-core",
+ "tower-sessions-memory-store",
+ "tracing",
+]
+
+[[package]]
+name = "tower-sessions-core"
+version = "0.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "568531ec3dfcf3ffe493de1958ae5662a0284ac5d767476ecdb6a34ff8c6b06c"
+dependencies = [
+ "async-trait",
+ "axum-core",
+ "base64",
+ "futures",
+ "http",
+ "parking_lot",
+ "rand 0.9.2",
+ "serde",
+ "serde_json",
+ "thiserror 2.0.18",
+ "time",
+ "tokio",
+ "tracing",
+]
+
+[[package]]
+name = "tower-sessions-memory-store"
+version = "0.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "713fabf882b6560a831e2bbed6204048b35bdd60e50bbb722902c74f8df33460"
+dependencies = [
+ "async-trait",
+ "time",
+ "tokio",
+ "tower-sessions-core",
+]
+
 [[package]]
 name = "tracing"
 version = "0.1.44"