feat(auth)!: ScadaBridge canonical roles + SoD collapse (Audit→Administrator, AuditReadOnly→Viewer) + config-DB migration (Task 1.7)

Standardize role string VALUES on the canonical vocabulary
(Administrator/Designer/Deployer/Viewer; Operator/Engineer unused here):
  Admin        -> Administrator
  Design       -> Designer
  Deployment   -> Deployer
  Audit        -> Administrator   (COLLAPSE; accepted privilege escalation)
  AuditReadOnly-> Viewer          (COLLAPSE; keeps audit-read, no export)

SoD: OperationalAuditRoles = { Administrator, Viewer },
     AuditExportRoles      = { Administrator }
so Viewer reads the audit log + nav but cannot bulk-export, while
Administrator does both + holds the full admin surface (the documented,
accepted auditor/admin SoD collapse).

Atomic move across every enforcement site:
- Roles constants; AuthorizationPolicies (RequireClaim values + SoD arrays +
  honest XML-doc); RoleMapper Deployer check.
- ManagementActor.GetRequiredRole switch + the hard-coded site-scope
  admin-bypass (now Roles.Administrator at all 6 sites). Site-scoping logic
  is otherwise unchanged.
- DebugStreamHub Administrator/Deployer gates (Deployer kept case-sensitive).
- CentralUI BrowseService/BindingTester Designer guards; LdapMappingForm
  dropdown now offers canonical values (incl. Viewer).
- Config-DB seed (LdapGroupMappings Id 1-4) + EF migration CanonicalizeRoles:
  Id-keyed UpdateData for seed rows + idempotent raw catch-all UPDATEs for
  operator-added rows. Down is lossy on the collapse (documented in-file).
  No pending model changes.

Tests reworked to the collapsed model across Security/CentralUI/
ManagementService/ConfigurationDatabase/Integration suites, incl. explicit
Viewer-reads-not-exports and former-Audit-now-Administrator-escalation cases.

CHANGELOG: BREAKING security note documenting the canonicalization + SoD
collapse.

CHANGELOG.md

@@ -6,6 +6,53 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
 
+### Changed — BREAKING: canonical role names + audit separation-of-duties collapse (Task 1.7)
+
+Role string VALUES are standardized onto the canonical vocabulary
+(`Administrator`/`Designer`/`Deployer`/`Viewer`; `Operator`/`Engineer` are unused
+by ScadaBridge). The legacy ScadaBridge role names were renamed and two were
+**collapsed**:
+
+| Legacy role     | Canonical role  | Notes |
+|-----------------|-----------------|-------|
+| `Admin`         | `Administrator` | rename |
+| `Design`        | `Designer`      | rename |
+| `Deployment`    | `Deployer`      | rename |
+| `Audit`         | `Administrator` | **COLLAPSE** |
+| `AuditReadOnly` | `Viewer`        | **COLLAPSE** |
+
+- **SECURITY — privilege escalation (accepted).** The former `Audit` role
+  collapses into `Administrator`. This is a real escalation: a former audit-only
+  user now holds the **entire admin surface** (create/update/delete sites, manage
+  LDAP group→role mappings and API keys, preview/import transport bundles), not
+  just audit read+export. This loss of auditor/admin separation-of-duties is a
+  deliberate, accepted trade-off of the canonicalization.
+- **SECURITY — half-SoD preserved.** The former `AuditReadOnly` role collapses
+  into `Viewer`, which **keeps audit READ** (Audit Log page, Configuration Audit
+  Log page, audit nav group) but **cannot bulk-export**. The audit policy sets are
+  now `OperationalAuditRoles = { Administrator, Viewer }` and
+  `AuditExportRoles = { Administrator }`, so a `Viewer` reads the audit log but the
+  Export-CSV button / `/api/audit/export` endpoint correctly refuses it.
+- **Enforcement.** Every enforcement site moved together: the role-claim values,
+  the authorization policies (`RequireAdmin`/`RequireDesign`/`RequireDeployment`
+  policy *names* are unchanged; only the role *values* inside them changed), the
+  `ManagementActor.GetRequiredRole` switch, the hard-coded site-scope admin-bypass
+  (`Roles.Administrator` everywhere), the `DebugStreamHub` Administrator/Deployer
+  gates, and the CentralUI `BrowseService`/`BindingTester` Designer guards.
+  **Site-scoping logic is otherwise unchanged** — only the admin-bypass *value*
+  moved from `"Admin"` to `Roles.Administrator`.
+- **Config-DB migration `CanonicalizeRoles`.** Updates the four seeded
+  `LdapGroupMappings` rows (Id 1-4) to the canonical role values and adds raw
+  idempotent catch-all `UPDATE`s for operator-added rows
+  (`Admin`/`Audit`→`Administrator`, `Design`→`Designer`, `Deployment`→`Deployer`,
+  `AuditReadOnly`→`Viewer`). The Down migration is **lossy** for the collapse: it
+  best-effort maps `Administrator`→`Admin` and `Viewer`→`AuditReadOnly` but cannot
+  recover the original `Audit`/`Admin` or `Viewer`/`AuditReadOnly` distinction.
+- **Operator action.** Any LDAP group→role mappings created with the legacy role
+  strings are migrated automatically by `CanonicalizeRoles`. New mappings created
+  via the CentralUI LDAP-mappings form now offer the canonical role values
+  (including a `Viewer` option for audit-read-only delegation).
+
 ### Changed — BREAKING: inbound API authentication
 
 Inbound API authentication has migrated off the SQL Server `X-API-Key` scheme and