feat: add flexible capability-based RBAC with per-tenant customization

Introduces a capability layer on top of existing roles that controls
feature visibility and access. Capabilities follow an area.feature.action
taxonomy (~35 capabilities) with sensible defaults per role. Tenant admins
can customize via grant/revoke overrides stored in org settings JSONB.

Key changes:
- Add vice_president role to DB schema
- Backend: capability constants, resolution logic, CapabilityGuard (global),
  @RequireCapability decorator on all 16 tenant controllers
- Frontend: permission hooks (useCanEdit, useHasCapability), CapabilityGate
  component, sidebar filtering by capability, all 17 pages migrated from
  useIsReadOnly to capability-based checks
- New admin UI: /settings/permissions matrix page for per-tenant role
  customization with grant/revoke delta model
- GET /organizations/my-capabilities endpoint for capability refresh
- Validation of permissionOverrides in settings updates

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

backend/src/common/permissions/resolve-permissions.ts

@@ -0,0 +1,57 @@
+import { ALL_CAPABILITIES } from './capabilities';
+import { DEFAULT_ROLE_CAPABILITIES } from './default-role-capabilities';
+
+export interface PermissionOverrides {
+  [role: string]: {
+    grant?: string[];
+    revoke?: string[];
+  };
+}
+
+/**
+ * Resolve effective capabilities for a role, applying tenant overrides.
+ *
+ * 1. Start with default capabilities for the role
+ * 2. Add any granted capabilities from overrides
+ * 3. Remove any revoked capabilities from overrides
+ *
+ * Unknown capabilities in grant/revoke are silently ignored (they may
+ * come from an older version of the overrides).
+ */
+export function resolveCapabilities(
+  role: string,
+  overrides?: PermissionOverrides | null,
+): Set<string> {
+  const defaults = DEFAULT_ROLE_CAPABILITIES[role] || [];
+  const result = new Set<string>(defaults);
+
+  if (overrides && overrides[role]) {
+    const roleOverride = overrides[role];
+
+    if (roleOverride.grant) {
+      for (const cap of roleOverride.grant) {
+        if (ALL_CAPABILITIES.has(cap)) {
+          result.add(cap);
+        }
+      }
+    }
+
+    if (roleOverride.revoke) {
+      for (const cap of roleOverride.revoke) {
+        result.delete(cap);
+      }
+    }
+  }
+
+  return result;
+}
+
+/**
+ * Convenience: resolve to a sorted array (for API responses).
+ */
+export function resolveCapabilitiesArray(
+  role: string,
+  overrides?: PermissionOverrides | null,
+): string[] {
+  return Array.from(resolveCapabilities(role, overrides)).sort();
+}