feat(sidecar): extend scoped proxy to web-client mutations, harden path classification

Batch archive/restore/delete/approve/private validate every UID against
the PhotoPrism DB in one query. Per-photo PUT/approve/like/stack-file
ops are ownership-checked. Admin-role sessions pass through fully so
settings/users/index dialogs keep working. Paths are unescaped+cleaned
before classification so encoded dot-segments can't smuggle past the
allowlist. Full httptest coverage of the routing decisions.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

sidecar/pp.go

@@ -90,6 +90,7 @@ func (c *ppClient) call(ctx context.Context, method, urlPath, token string, body
 type ppSessionUser struct {
 	UserUID  string `json:"UID"`
 	UserName string `json:"Name"`
+	Role     string `json:"Role"`
 	BasePath string `json:"BasePath"`
 }