feat(auth): add authentication, RBAC, API tokens, and default admin

Add a complete authentication and authorization system to Silo with
three pluggable backends (local bcrypt, LDAP/FreeIPA, OIDC/Keycloak),
session management, API token support, and role-based access control.

Authentication backends:
- Local: bcrypt (cost 12) password verification against users table
- LDAP: FreeIPA simple bind with group-to-role mapping
- OIDC: Keycloak redirect flow with realm role mapping
- Backends are tried in order; users upserted to DB on first login

Session and token management:
- PostgreSQL-backed sessions via alexedwards/scs + pgxstore
- Opaque API tokens (silo_ prefix, SHA-256 hashed, shown once)
- 24h session lifetime, HttpOnly/SameSite=Lax/Secure cookies

Role-based access control (admin > editor > viewer):
- RequireAuth middleware: Bearer token -> session -> redirect/401
- RequireRole middleware: per-route-group minimum role enforcement
- CSRF protection via justinas/nosurf on web forms, API exempt
- CORS locked to configured origins when auth enabled

Route restructuring:
- Public: /health, /ready, /login, /auth/oidc, /auth/callback
- Web (auth + CSRF): /, /projects, /schemas, /settings
- API read (viewer): GET /api/**
- API write (editor): POST/PUT/PATCH/DELETE /api/**

User context wiring:
- created_by/updated_by columns on items, projects, relationships
- All create/update handlers populate tracking fields from context
- CSV and BOM import handlers pass authenticated username
- Revision creation tracks user across all code paths

Default admin account:
- Configurable via auth.local.default_admin_username/password
- Env var overrides: SILO_ADMIN_USERNAME, SILO_ADMIN_PASSWORD
- Idempotent: created on first startup, skipped if exists

CLI and FreeCAD plugin:
- silo token create/list/revoke subcommands (HTTP API client)
- FreeCAD SiloClient sends Bearer token on all requests
- Token read from ApiToken preference or SILO_API_TOKEN env var

Web UI:
- Login page (Catppuccin Mocha themed, OIDC button conditional)
- Settings page with account info and API token management
- User display name, role badge, and logout button in header
- One-time token display banner with copy-to-clipboard

Database (migration 009):
- users table with role, auth_source, oidc_subject, password_hash
- api_tokens table with SHA-256 hash, prefix, expiry, scopes
- sessions table (scs pgxstore schema)
- audit_log table (schema ready for future use)
- created_by/updated_by ALTER on items, relationships, projects

New dependencies: scs/v2, scs/pgxstore, go-oidc/v3, go-ldap/v3,
justinas/nosurf, golang.org/x/oauth2

deployments/config.prod.yaml

@@ -35,3 +35,48 @@ schemas:
 freecad:
   uri_scheme: "silo"
   executable: "/usr/bin/freecad"
+
+# Authentication
+# Set via SILO_SESSION_SECRET, SILO_OIDC_CLIENT_SECRET, SILO_LDAP_BIND_PASSWORD env vars
+auth:
+  enabled: true
+  session_secret: "" # Set via SILO_SESSION_SECRET
+
+  local:
+    enabled: true
+    default_admin_username: "admin"
+    default_admin_password: "" # Set via SILO_ADMIN_PASSWORD
+
+  ldap:
+    enabled: true
+    url: "ldaps://ipa.kindred.internal"
+    base_dn: "dc=kindred,dc=internal"
+    user_search_dn: "cn=users,cn=accounts,dc=kindred,dc=internal"
+    user_attr: "uid"
+    email_attr: "mail"
+    display_attr: "displayName"
+    group_attr: "memberOf"
+    role_mapping:
+      admin:
+        - "cn=silo-admins,cn=groups,cn=accounts,dc=kindred,dc=internal"
+      editor:
+        - "cn=silo-users,cn=groups,cn=accounts,dc=kindred,dc=internal"
+        - "cn=engineers,cn=groups,cn=accounts,dc=kindred,dc=internal"
+      viewer:
+        - "cn=silo-viewers,cn=groups,cn=accounts,dc=kindred,dc=internal"
+    tls_skip_verify: false
+
+  oidc:
+    enabled: false
+    issuer_url: "https://keycloak.kindred.internal/realms/silo"
+    client_id: "silo"
+    client_secret: "" # Set via SILO_OIDC_CLIENT_SECRET
+    redirect_url: "https://silo.kindred.internal/auth/callback"
+    scopes: ["openid", "profile", "email"]
+    admin_role: "silo-admin"
+    editor_role: "silo-editor"
+    default_role: "viewer"
+
+  cors:
+    allowed_origins:
+      - "https://silo.kindred.internal"

deployments/docker-compose.yaml

@@ -60,6 +60,11 @@ services:
       SILO_MINIO_SECRET_KEY: ${MINIO_SECRET_KEY:-silominiosecret}
       SILO_MINIO_BUCKET: silo-files
       SILO_MINIO_USE_SSL: "false"
+      SILO_SESSION_SECRET: ${SILO_SESSION_SECRET:-change-me-in-production}
+      SILO_OIDC_CLIENT_SECRET: ${SILO_OIDC_CLIENT_SECRET:-}
+      SILO_LDAP_BIND_PASSWORD: ${SILO_LDAP_BIND_PASSWORD:-}
+      SILO_ADMIN_USERNAME: ${SILO_ADMIN_USERNAME:-admin}
+      SILO_ADMIN_PASSWORD: ${SILO_ADMIN_PASSWORD:-}
     ports:
       - "8080:8080"
     volumes: